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 $57.44   13.262%   $65.0577   $65.06   $65.05   $65.10  
  Purchase #2 $89.38   8.789%   $97.2356   $97.24   $97.25   $97.20  
  Purchase #3 $244.97   6.355%   $260.5378   $260.54   $260.55   $260.50  
  Purchase #4 $190.70   11.481%   $212.5943   $212.59   $212.60   $212.60  
  Purchase #5 $21.49   9.831%   $23.6027   $23.60   $23.60   $23.60  
  Purchase #6 $230.37   11.313%   $256.4318   $256.43   $256.45   $256.40  
  Purchase #7 $31.71   9.275%   $34.6511   $34.65   $34.65   $34.70  
  7 purchase totals = $866.06       $950.1110   $950.11   $950.15   $950.10