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 $62.63   9.412%   $68.5247   $68.52   $68.50   $68.50  
  Purchase #2 $221.89   11.420%   $247.2298   $247.23   $247.25   $247.20  
  Purchase #3 $23.38   8.237%   $25.3058   $25.31   $25.30   $25.30  
  Purchase #4 $34.66   9.423%   $37.926   $37.93   $37.95   $37.90  
  Purchase #5 $196.35   5.148%   $206.4581   $206.46   $206.45   $206.50  
  Purchase #6 $46.48   9.789%   $51.0299   $51.03   $51.05   $51.00  
  Purchase #7 $232.41   9.797%   $255.1792   $255.18   $255.20   $255.20  
  7 purchase totals = $817.80       $891.6535   $891.66   $891.70   $891.60