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 $205.51   10.274%   $226.6241   $226.62   $226.60   $226.60  
  Purchase #2 $47.69   9.447%   $52.1953   $52.20   $52.20   $52.20  
  Purchase #3 $148.47   7.350%   $159.3825   $159.38   $159.40   $159.40  
  Purchase #4 $162.85   8.476%   $176.6532   $176.65   $176.65   $176.70  
  Purchase #5 $71.42   13.353%   $80.9567   $80.96   $80.95   $81.00  
  Purchase #6 $135.54   11.756%   $151.4741   $151.47   $151.45   $151.50  
  Purchase #7 $242.63   6.416%   $258.1971   $258.20   $258.20   $258.20  
  7 purchase totals = $1,014.11       $1,105.4830   $1,105.48   $1,105.45   $1,105.60