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 $119.28   12.502%   $134.1924   $134.19   $134.20   $134.20  
  Purchase #2 $49.91   8.134%   $53.9697   $53.97   $53.95   $54.00  
  Purchase #3 $25.73   10.689%   $28.4803   $28.48   $28.50   $28.50  
  Purchase #4 $24.72   7.446%   $26.5607   $26.56   $26.55   $26.60  
  Purchase #5 $221.53   13.319%   $251.0356   $251.04   $251.05   $251.00  
  Purchase #6 $159.59   4.665%   $167.0349   $167.03   $167.05   $167.00  
  Purchase #7 $157.41   3.621%   $163.1098   $163.11   $163.10   $163.10  
  7 purchase totals = $758.17       $824.3834   $824.38   $824.40   $824.40