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 $195.48   3.621%   $202.5583   $202.56   $202.55   $202.60  
  Purchase #2 $97.97   10.577%   $108.3323   $108.33   $108.35   $108.30  
  Purchase #3 $135.84   8.131%   $146.8852   $146.89   $146.90   $146.90  
  Purchase #4 $239.36   9.790%   $262.7933   $262.79   $262.80   $262.80  
  Purchase #5 $61.41   13.540%   $69.7249   $69.72   $69.70   $69.70  
  Purchase #6 $134.44   3.628%   $139.3175   $139.32   $139.30   $139.30  
  Purchase #7 $22.42   7.125%   $24.0174   $24.02   $24.00   $24.00  
  7 purchase totals = $886.92       $953.6289   $953.63   $953.60   $953.60