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 $46.30   7.845%   $49.9322   $49.93   $49.95   $49.90  
  Purchase #2 $232.58   10.625%   $257.2916   $257.29   $257.30   $257.30  
  Purchase #3 $62.90   13.851%   $71.6123   $71.61   $71.60   $71.60  
  Purchase #4 $220.70   8.274%   $238.9607   $238.96   $238.95   $239.00  
  Purchase #5 $125.83   10.484%   $139.022   $139.02   $139.00   $139.00  
  Purchase #6 $97.60   13.556%   $110.8307   $110.83   $110.85   $110.80  
  Purchase #7 $128.86   7.636%   $138.6997   $138.70   $138.70   $138.70  
  7 purchase totals = $914.77       $1,006.3492   $1,006.34   $1,006.35   $1,006.30