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 $57.26   6.550%   $61.0105   $61.01   $61.00   $61.00  
  Purchase #2 $244.84   9.375%   $267.7938   $267.79   $267.80   $267.80  
  Purchase #3 $32.76   8.384%   $35.5066   $35.51   $35.50   $35.50  
  Purchase #4 $124.25   9.626%   $136.2103   $136.21   $136.20   $136.20  
  Purchase #5 $94.72   7.867%   $102.1716   $102.17   $102.15   $102.20  
  Purchase #6 $74.50   9.430%   $81.5254   $81.53   $81.55   $81.50  
  Purchase #7 $227.70   12.434%   $256.0122   $256.01   $256.00   $256.00  
  7 purchase totals = $856.03       $940.2304   $940.23   $940.20   $940.20