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 $48.34   5.267%   $50.8861   $50.89   $50.90   $50.90  
  Purchase #2 $221.64   13.544%   $251.6589   $251.66   $251.65   $251.70  
  Purchase #3 $118.44   7.484%   $127.304   $127.30   $127.30   $127.30  
  Purchase #4 $82.57   8.784%   $89.8229   $89.82   $89.80   $89.80  
  Purchase #5 $212.84   10.693%   $235.599   $235.60   $235.60   $235.60  
  Purchase #6 $9.70   13.434%   $11.0031   $11.00   $11.00   $11.00  
  Purchase #7 $87.49   9.437%   $95.7464   $95.75   $95.75   $95.70  
  7 purchase totals = $781.02       $862.0204   $862.02   $862.00   $862.00