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 $65.67   4.523%   $68.6403   $68.64   $68.65   $68.60  
  Purchase #2 $206.87   13.289%   $234.361   $234.36   $234.35   $234.40  
  Purchase #3 $61.64   6.638%   $65.7317   $65.73   $65.75   $65.70  
  Purchase #4 $231.77   5.172%   $243.7571   $243.76   $243.75   $243.80  
  Purchase #5 $201.55   13.499%   $228.7572   $228.76   $228.75   $228.80  
  Purchase #6 $32.79   6.395%   $34.8869   $34.89   $34.90   $34.90  
  Purchase #7 $71.95   9.403%   $78.7155   $78.72   $78.70   $78.70  
  7 purchase totals = $872.24       $954.8497   $954.86   $954.85   $954.90