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 $250.69   12.646%   $282.3923   $282.39   $282.40   $282.40  
  Purchase #2 $221.39   4.443%   $231.2264   $231.23   $231.25   $231.20  
  Purchase #3 $104.37   5.525%   $110.1364   $110.14   $110.15   $110.10  
  Purchase #4 $54.96   3.306%   $56.777   $56.78   $56.80   $56.80  
  Purchase #5 $226.67   8.816%   $246.6532   $246.65   $246.65   $246.70  
  Purchase #6 $118.30   13.251%   $133.9759   $133.98   $134.00   $134.00  
  Purchase #7 $209.64   11.706%   $234.1805   $234.18   $234.20   $234.20  
  7 purchase totals = $1,186.02       $1,295.3417   $1,295.35   $1,295.45   $1,295.40