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 $54.79   5.383%   $57.7393   $57.74   $57.75   $57.70  
  Purchase #2 $237.31   9.415%   $259.6527   $259.65   $259.65   $259.70  
  Purchase #3 $61.39   7.428%   $65.95   $65.95   $65.95   $66.00  
  Purchase #4 $97.54   13.765%   $110.9664   $110.97   $110.95   $111.00  
  Purchase #5 $199.85   12.677%   $225.185   $225.19   $225.20   $225.20  
  Purchase #6 $133.98   6.185%   $142.2667   $142.27   $142.25   $142.30  
  Purchase #7 $220.92   10.402%   $243.9001   $243.90   $243.90   $243.90  
  7 purchase totals = $1,005.78       $1,105.6602   $1,105.67   $1,105.65   $1,105.80