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 $125.30   3.613%   $129.8271   $129.83   $129.85   $129.80  
  Purchase #2 $210.94   11.126%   $234.4092   $234.41   $234.40   $234.40  
  Purchase #3 $39.81   12.288%   $44.7019   $44.70   $44.70   $44.70  
  Purchase #4 $81.92   9.146%   $89.4124   $89.41   $89.40   $89.40  
  Purchase #5 $65.30   5.331%   $68.7811   $68.78   $68.80   $68.80  
  Purchase #6 $223.32   10.323%   $246.3733   $246.37   $246.35   $246.40  
  Purchase #7 $69.72   8.484%   $75.635   $75.64   $75.65   $75.60  
  7 purchase totals = $816.31       $889.1400   $889.14   $889.15   $889.10