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 $225.75   9.121%   $246.3407   $246.34   $246.35   $246.30  
  Purchase #2 $194.69   3.646%   $201.7884   $201.79   $201.80   $201.80  
  Purchase #3 $83.52   13.727%   $94.9848   $94.98   $95.00   $95.00  
  Purchase #4 $161.38   12.837%   $182.0964   $182.10   $182.10   $182.10  
  Purchase #5 $247.99   10.332%   $273.6123   $273.61   $273.60   $273.60  
  Purchase #6 $221.73   6.306%   $235.7123   $235.71   $235.70   $235.70  
  Purchase #7 $53.71   8.458%   $58.2528   $58.25   $58.25   $58.30  
  7 purchase totals = $1,188.77       $1,292.7877   $1,292.78   $1,292.80   $1,292.80