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 $87.92   11.697%   $98.204   $98.20   $98.20   $98.20  
  Purchase #2 $121.64   13.168%   $137.6576   $137.66   $137.65   $137.70  
  Purchase #3 $179.95   11.137%   $199.991   $199.99   $200.00   $200.00  
  Purchase #4 $220.60   11.871%   $246.7874   $246.79   $246.80   $246.80  
  Purchase #5 $66.54   7.595%   $71.5937   $71.59   $71.60   $71.60  
  Purchase #6 $210.59   12.218%   $236.3199   $236.32   $236.30   $236.30  
  Purchase #7 $153.67   3.850%   $159.5863   $159.59   $159.60   $159.60  
  7 purchase totals = $1,040.91       $1,150.1399   $1,150.14   $1,150.15   $1,150.20