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 $249.66   5.852%   $264.2701   $264.27   $264.25   $264.30  
  Purchase #2 $82.53   10.426%   $91.1346   $91.13   $91.15   $91.10  
  Purchase #3 $77.81   12.600%   $87.6141   $87.61   $87.60   $87.60  
  Purchase #4 $119.46   8.650%   $129.7933   $129.79   $129.80   $129.80  
  Purchase #5 $165.36   9.439%   $180.9683   $180.97   $180.95   $181.00  
  Purchase #6 $13.91   5.125%   $14.6229   $14.62   $14.60   $14.60  
  Purchase #7 $141.33   12.566%   $159.0895   $159.09   $159.10   $159.10  
  7 purchase totals = $850.06       $927.4928   $927.48   $927.45   $927.50