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 $237.25   6.308%   $252.2157   $252.22   $252.20   $252.20  
  Purchase #2 $67.67   6.725%   $72.2208   $72.22   $72.20   $72.20  
  Purchase #3 $219.79   13.362%   $249.1583   $249.16   $249.15   $249.20  
  Purchase #4 $36.70   12.665%   $41.3481   $41.35   $41.35   $41.30  
  Purchase #5 $97.95   5.462%   $103.3   $103.30   $103.30   $103.30  
  Purchase #6 $25.32   12.446%   $28.4713   $28.47   $28.45   $28.50  
  Purchase #7 $246.61   8.781%   $268.2648   $268.26   $268.25   $268.30  
  7 purchase totals = $931.29       $1,014.9790   $1,014.98   $1,014.90   $1,015.00