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 $189.98   6.293%   $201.9354   $201.94   $201.95   $201.90  
  Purchase #2 $65.55   13.232%   $74.2236   $74.22   $74.20   $74.20  
  Purchase #3 $12.45   8.714%   $13.5349   $13.53   $13.55   $13.50  
  Purchase #4 $162.64   10.807%   $180.2165   $180.22   $180.20   $180.20  
  Purchase #5 $49.53   3.838%   $51.431   $51.43   $51.45   $51.40  
  Purchase #6 $91.92   7.199%   $98.5373   $98.54   $98.55   $98.50  
  Purchase #7 $54.99   4.310%   $57.3601   $57.36   $57.35   $57.40  
  7 purchase totals = $627.06       $677.2388   $677.24   $677.25   $677.10