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 $191.75   6.419%   $204.0584   $204.06   $204.05   $204.10  
  Purchase #2 $45.51   11.867%   $50.9107   $50.91   $50.90   $50.90  
  Purchase #3 $27.77   12.371%   $31.2054   $31.21   $31.20   $31.20  
  Purchase #4 $203.60   11.616%   $227.2502   $227.25   $227.25   $227.30  
  Purchase #5 $67.77   5.683%   $71.6214   $71.62   $71.60   $71.60  
  Purchase #6 $198.37   11.161%   $220.5101   $220.51   $220.50   $220.50  
  Purchase #7 $67.70   5.399%   $71.3551   $71.36   $71.35   $71.40  
  7 purchase totals = $802.47       $876.9113   $876.92   $876.85   $877.00