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 $108.78   9.647%   $119.274   $119.27   $119.25   $119.30  
  Purchase #2 $92.43   4.568%   $96.6522   $96.65   $96.65   $96.70  
  Purchase #3 $122.41   7.829%   $131.9935   $131.99   $132.00   $132.00  
  Purchase #4 $80.95   8.847%   $88.1116   $88.11   $88.10   $88.10  
  Purchase #5 $13.89   11.703%   $15.5155   $15.52   $15.50   $15.50  
  Purchase #6 $43.87   4.229%   $45.7253   $45.73   $45.75   $45.70  
  Purchase #7 $69.55   13.873%   $79.1987   $79.20   $79.20   $79.20  
  7 purchase totals = $531.88       $576.4708   $576.47   $576.45   $576.50