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 $193.32   13.293%   $219.018   $219.02   $219.00   $219.00  
  Purchase #2 $63.40   8.126%   $68.5519   $68.55   $68.55   $68.60  
  Purchase #3 $173.51   12.547%   $195.2803   $195.28   $195.30   $195.30  
  Purchase #4 $148.45   4.419%   $155.01   $155.01   $155.00   $155.00  
  Purchase #5 $128.31   4.682%   $134.3175   $134.32   $134.30   $134.30  
  Purchase #6 $59.97   7.660%   $64.5637   $64.56   $64.55   $64.60  
  Purchase #7 $164.72   9.293%   $180.0274   $180.03   $180.05   $180.00  
  7 purchase totals = $931.68       $1,016.7688   $1,016.77   $1,016.75   $1,016.80