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 $173.73   12.210%   $194.9424   $194.94   $194.95   $194.90  
  Purchase #2 $227.54   4.407%   $237.5677   $237.57   $237.55   $237.60  
  Purchase #3 $90.99   8.864%   $99.0554   $99.06   $99.05   $99.10  
  Purchase #4 $43.49   7.654%   $46.8187   $46.82   $46.80   $46.80  
  Purchase #5 $244.43   11.481%   $272.493   $272.49   $272.50   $272.50  
  Purchase #6 $53.55   10.593%   $59.2226   $59.22   $59.20   $59.20  
  Purchase #7 $115.33   8.409%   $125.0281   $125.03   $125.05   $125.00  
  7 purchase totals = $949.06       $1,035.1279   $1,035.13   $1,035.10   $1,035.10