Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $120.48   10.409%   $133.0208   $133.02   $133.00   $133.00  
  Purchase #2 $170.54   5.381%   $179.7168   $179.72   $179.70   $179.70  
  Purchase #3 $119.97   5.313%   $126.344   $126.34   $126.35   $126.30  
  Purchase #4 $211.90   9.637%   $232.3208   $232.32   $232.30   $232.30  
  Purchase #5 $187.95   8.264%   $203.4822   $203.48   $203.50   $203.50  
  Purchase #6 $198.91   4.543%   $207.9465   $207.95   $207.95   $207.90  
  Purchase #7 $248.57   9.671%   $272.6092   $272.61   $272.60   $272.60  
  7 purchase totals = $1,258.32       $1,355.4403   $1,355.44   $1,355.40   $1,355.30