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 $44.84   7.821%   $48.3469   $48.35   $48.35   $48.30  
  Purchase #2 $95.64   11.183%   $106.3354   $106.34   $106.35   $106.30  
  Purchase #3 $51.31   6.113%   $54.4466   $54.45   $54.45   $54.40  
  Purchase #4 $193.33   4.395%   $201.8269   $201.83   $201.85   $201.80  
  Purchase #5 $164.99   7.352%   $177.1201   $177.12   $177.10   $177.10  
  Purchase #6 $37.50   10.285%   $41.3569   $41.36   $41.35   $41.40  
  Purchase #7 $81.44   13.535%   $92.4629   $92.46   $92.45   $92.50  
  7 purchase totals = $669.05       $721.8957   $721.91   $721.90   $721.80