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 $48.38   12.212%   $54.2882   $54.29   $54.30   $54.30  
  Purchase #2 $83.86   13.273%   $94.9907   $94.99   $95.00   $95.00  
  Purchase #3 $134.87   12.840%   $152.1873   $152.19   $152.20   $152.20  
  Purchase #4 $88.85   9.145%   $96.9753   $96.98   $97.00   $97.00  
  Purchase #5 $36.89   12.318%   $41.4341   $41.43   $41.45   $41.40  
  Purchase #6 $175.92   11.395%   $195.9661   $195.97   $195.95   $196.00  
  Purchase #7 $66.36   10.786%   $73.5176   $73.52   $73.50   $73.50  
  7 purchase totals = $635.13       $709.3593   $709.37   $709.40   $709.40