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 $110.51   8.162%   $119.5298   $119.53   $119.55   $119.50  
  Purchase #2 $184.75   10.799%   $204.7012   $204.70   $204.70   $204.70  
  Purchase #3 $93.94   12.169%   $105.3716   $105.37   $105.35   $105.40  
  Purchase #4 $167.42   6.259%   $177.8988   $177.90   $177.90   $177.90  
  Purchase #5 $202.47   13.367%   $229.5342   $229.53   $229.55   $229.50  
  Purchase #6 $189.26   9.303%   $206.8669   $206.87   $206.85   $206.90  
  Purchase #7 $219.85   4.770%   $230.3368   $230.34   $230.35   $230.30  
  7 purchase totals = $1,168.20       $1,274.2393   $1,274.24   $1,274.25   $1,274.20