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 $62.47   6.779%   $66.7048   $66.70   $66.70   $66.70  
  Purchase #2 $211.83   13.606%   $240.6516   $240.65   $240.65   $240.70  
  Purchase #3 $79.35   5.373%   $83.6135   $83.61   $83.60   $83.60  
  Purchase #4 $100.72   7.812%   $108.5882   $108.59   $108.60   $108.60  
  Purchase #5 $41.37   10.793%   $45.8351   $45.84   $45.85   $45.80  
  Purchase #6 $213.85   6.112%   $226.9205   $226.92   $226.90   $226.90  
  Purchase #7 $121.87   8.553%   $132.2935   $132.29   $132.30   $132.30  
  7 purchase totals = $831.46       $904.6072   $904.60   $904.60   $904.60