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 $146.38   12.453%   $164.6087   $164.61   $164.60   $164.60  
  Purchase #2 $62.51   8.831%   $68.0303   $68.03   $68.05   $68.00  
  Purchase #3 $128.80   3.639%   $133.487   $133.49   $133.50   $133.50  
  Purchase #4 $31.81   7.170%   $34.0908   $34.09   $34.10   $34.10  
  Purchase #5 $95.81   10.837%   $106.1929   $106.19   $106.20   $106.20  
  Purchase #6 $197.56   10.532%   $218.367   $218.37   $218.35   $218.40  
  Purchase #7 $63.53   8.670%   $69.0381   $69.04   $69.05   $69.00  
  7 purchase totals = $726.40       $793.8148   $793.82   $793.85   $793.80