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 $143.29   4.867%   $150.2639   $150.26   $150.25   $150.30  
  Purchase #2 $120.26   4.369%   $125.5142   $125.51   $125.50   $125.50  
  Purchase #3 $79.98   7.421%   $85.9153   $85.92   $85.90   $85.90  
  Purchase #4 $125.69   9.736%   $137.9272   $137.93   $137.95   $137.90  
  Purchase #5 $216.68   9.711%   $237.7218   $237.72   $237.70   $237.70  
  Purchase #6 $62.80   9.389%   $68.6963   $68.70   $68.70   $68.70  
  Purchase #7 $35.32   10.712%   $39.1035   $39.10   $39.10   $39.10  
  7 purchase totals = $784.02       $845.1422   $845.14   $845.10   $845.10