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 $59.99   12.824%   $67.6831   $67.68   $67.70   $67.70  
  Purchase #2 $156.77   4.203%   $163.359   $163.36   $163.35   $163.40  
  Purchase #3 $74.91   3.304%   $77.385   $77.39   $77.40   $77.40  
  Purchase #4 $249.61   10.715%   $276.3557   $276.36   $276.35   $276.40  
  Purchase #5 $201.43   12.114%   $225.8312   $225.83   $225.85   $225.80  
  Purchase #6 $105.58   5.470%   $111.3552   $111.36   $111.35   $111.40  
  Purchase #7 $8.97   12.776%   $10.116   $10.12   $10.10   $10.10  
  7 purchase totals = $857.26       $932.0852   $932.10   $932.10   $932.20