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 $61.89   13.401%   $70.1839   $70.18   $70.20   $70.20  
  Purchase #2 $245.69   4.319%   $256.3014   $256.30   $256.30   $256.30  
  Purchase #3 $243.67   3.165%   $251.3822   $251.38   $251.40   $251.40  
  Purchase #4 $58.57   4.261%   $61.0657   $61.07   $61.05   $61.10  
  Purchase #5 $123.43   4.280%   $128.7128   $128.71   $128.70   $128.70  
  Purchase #6 $203.96   6.348%   $216.9074   $216.91   $216.90   $216.90  
  Purchase #7 $141.73   6.418%   $150.8262   $150.83   $150.85   $150.80  
  7 purchase totals = $1,078.94       $1,135.3796   $1,135.38   $1,135.40   $1,135.40