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 $62.41   12.454%   $70.1825   $70.18   $70.20   $70.20  
  Purchase #2 $194.92   5.821%   $206.2663   $206.27   $206.25   $206.30  
  Purchase #3 $35.48   12.169%   $39.7976   $39.80   $39.80   $39.80  
  Purchase #4 $24.26   7.861%   $26.1671   $26.17   $26.15   $26.20  
  Purchase #5 $111.79   8.618%   $121.4241   $121.42   $121.40   $121.40  
  Purchase #6 $133.53   6.237%   $141.8583   $141.86   $141.85   $141.90  
  Purchase #7 $111.44   13.580%   $126.5736   $126.57   $126.55   $126.60  
  7 purchase totals = $673.83       $732.2695   $732.27   $732.20   $732.40