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 $61.93   5.363%   $65.2513   $65.25   $65.25   $65.30  
  Purchase #2 $104.97   12.643%   $118.2414   $118.24   $118.25   $118.20  
  Purchase #3 $135.71   11.614%   $151.4714   $151.47   $151.45   $151.50  
  Purchase #4 $147.65   5.124%   $155.2156   $155.22   $155.20   $155.20  
  Purchase #5 $148.89   7.760%   $160.4439   $160.44   $160.45   $160.40  
  Purchase #6 $189.79   8.601%   $206.1138   $206.11   $206.10   $206.10  
  Purchase #7 $201.31   11.641%   $224.7445   $224.74   $224.75   $224.70  
  7 purchase totals = $990.25       $1,081.4819   $1,081.47   $1,081.45   $1,081.40