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 $56.33   5.162%   $59.2378   $59.24   $59.25   $59.20  
  Purchase #2 $188.42   9.533%   $206.3821   $206.38   $206.40   $206.40  
  Purchase #3 $182.48   4.869%   $191.365   $191.37   $191.35   $191.40  
  Purchase #4 $210.44   12.470%   $236.6819   $236.68   $236.70   $236.70  
  Purchase #5 $187.34   10.499%   $207.0088   $207.01   $207.00   $207.00  
  Purchase #6 $41.36   6.853%   $44.1944   $44.19   $44.20   $44.20  
  Purchase #7 $96.87   10.108%   $106.6616   $106.66   $106.65   $106.70  
  7 purchase totals = $963.24       $1,051.5316   $1,051.53   $1,051.55   $1,051.60