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 $206.92   12.427%   $232.6339   $232.63   $232.65   $232.60  
  Purchase #2 $208.67   12.306%   $234.3489   $234.35   $234.35   $234.30  
  Purchase #3 $67.79   11.795%   $75.7858   $75.79   $75.80   $75.80  
  Purchase #4 $106.50   3.113%   $109.8153   $109.82   $109.80   $109.80  
  Purchase #5 $41.31   13.687%   $46.9641   $46.96   $46.95   $47.00  
  Purchase #6 $221.31   9.528%   $242.3964   $242.40   $242.40   $242.40  
  Purchase #7 $25.90   12.384%   $29.1075   $29.11   $29.10   $29.10  
  7 purchase totals = $878.40       $971.0519   $971.06   $971.05   $971.00