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 $219.61   8.226%   $237.6751   $237.68   $237.70   $237.70  
  Purchase #2 $56.79   6.722%   $60.6074   $60.61   $60.60   $60.60  
  Purchase #3 $145.53   11.417%   $162.1452   $162.15   $162.15   $162.10  
  Purchase #4 $23.49   3.850%   $24.3944   $24.39   $24.40   $24.40  
  Purchase #5 $23.89   3.510%   $24.7285   $24.73   $24.75   $24.70  
  Purchase #6 $135.80   8.172%   $146.8976   $146.90   $146.90   $146.90  
  Purchase #7 $68.87   12.674%   $77.5986   $77.60   $77.60   $77.60  
  7 purchase totals = $673.98       $734.0468   $734.06   $734.10   $734.00