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 $96.57   11.591%   $107.7634   $107.76   $107.75   $107.80  
  Purchase #2 $39.53   11.297%   $43.9957   $44.00   $44.00   $44.00  
  Purchase #3 $20.51   8.390%   $22.2308   $22.23   $22.25   $22.20  
  Purchase #4 $58.25   5.266%   $61.3174   $61.32   $61.30   $61.30  
  Purchase #5 $217.80   8.345%   $235.9754   $235.98   $236.00   $236.00  
  Purchase #6 $228.67   11.237%   $254.3656   $254.37   $254.35   $254.40  
  Purchase #7 $243.32   9.643%   $266.7833   $266.78   $266.80   $266.80  
  7 purchase totals = $904.65       $992.4316   $992.44   $992.45   $992.50