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 $65.56   5.283%   $69.0235   $69.02   $69.00   $69.00  
  Purchase #2 $156.55   4.369%   $163.3897   $163.39   $163.40   $163.40  
  Purchase #3 $247.80   3.525%   $256.535   $256.54   $256.55   $256.50  
  Purchase #4 $103.35   4.221%   $107.7124   $107.71   $107.70   $107.70  
  Purchase #5 $19.43   6.598%   $20.712   $20.71   $20.70   $20.70  
  Purchase #6 $247.65   3.211%   $255.602   $255.60   $255.60   $255.60  
  Purchase #7 $143.87   4.534%   $150.3931   $150.39   $150.40   $150.40  
  7 purchase totals = $984.21       $1,023.3677   $1,023.36   $1,023.35   $1,023.30