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 $194.66   4.159%   $202.7559   $202.76   $202.75   $202.80  
  Purchase #2 $15.30   13.450%   $17.3579   $17.36   $17.35   $17.40  
  Purchase #3 $48.64   10.198%   $53.6003   $53.60   $53.60   $53.60  
  Purchase #4 $245.46   10.175%   $270.4356   $270.44   $270.45   $270.40  
  Purchase #5 $210.75   6.781%   $225.041   $225.04   $225.05   $225.00  
  Purchase #6 $70.66   4.753%   $74.0185   $74.02   $74.00   $74.00  
  Purchase #7 $11.29   7.500%   $12.1368   $12.14   $12.15   $12.10  
  7 purchase totals = $796.76       $855.3460   $855.36   $855.35   $855.30