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 $113.27   4.204%   $118.0319   $118.03   $118.05   $118.00  
  Purchase #2 $28.76   11.255%   $31.9969   $32.00   $32.00   $32.00  
  Purchase #3 $207.43   4.779%   $217.3431   $217.34   $217.35   $217.30  
  Purchase #4 $32.32   9.109%   $35.264   $35.26   $35.25   $35.30  
  Purchase #5 $244.87   7.661%   $263.6295   $263.63   $263.65   $263.60  
  Purchase #6 $216.25   8.501%   $234.6334   $234.63   $234.65   $234.60  
  Purchase #7 $128.52   7.813%   $138.5613   $138.56   $138.55   $138.60  
  7 purchase totals = $971.42       $1,039.4601   $1,039.45   $1,039.50   $1,039.40