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 $242.89   11.863%   $271.704   $271.70   $271.70   $271.70  
  Purchase #2 $21.67   8.131%   $23.432   $23.43   $23.45   $23.40  
  Purchase #3 $139.78   8.730%   $151.9828   $151.98   $152.00   $152.00  
  Purchase #4 $232.35   9.861%   $255.262   $255.26   $255.25   $255.30  
  Purchase #5 $167.61   8.178%   $181.3171   $181.32   $181.30   $181.30  
  Purchase #6 $230.29   6.106%   $244.3515   $244.35   $244.35   $244.40  
  Purchase #7 $147.76   13.134%   $167.1668   $167.17   $167.15   $167.20  
  7 purchase totals = $1,182.35       $1,295.2162   $1,295.21   $1,295.20   $1,295.30