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 $190.90   6.309%   $202.9439   $202.94   $202.95   $202.90  
  Purchase #2 $143.27   11.584%   $159.8664   $159.87   $159.85   $159.90  
  Purchase #3 $68.91   6.627%   $73.4767   $73.48   $73.50   $73.50  
  Purchase #4 $176.86   13.692%   $201.0757   $201.08   $201.10   $201.10  
  Purchase #5 $249.40   9.637%   $273.4347   $273.43   $273.45   $273.40  
  Purchase #6 $202.35   4.511%   $211.478   $211.48   $211.50   $211.50  
  Purchase #7 $114.84   8.120%   $124.165   $124.17   $124.15   $124.20  
  7 purchase totals = $1,146.53       $1,246.4404   $1,246.45   $1,246.50   $1,246.50