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 $213.62   6.635%   $227.7937   $227.79   $227.80   $227.80  
  Purchase #2 $54.95   12.241%   $61.6764   $61.68   $61.70   $61.70  
  Purchase #3 $80.73   9.709%   $88.5681   $88.57   $88.55   $88.60  
  Purchase #4 $116.57   12.637%   $131.301   $131.30   $131.30   $131.30  
  Purchase #5 $240.46   10.346%   $265.338   $265.34   $265.35   $265.30  
  Purchase #6 $124.36   7.734%   $133.978   $133.98   $134.00   $134.00  
  Purchase #7 $13.56   10.193%   $14.9422   $14.94   $14.95   $14.90  
  7 purchase totals = $844.25       $923.5974   $923.60   $923.65   $923.60