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 $47.95   7.408%   $51.5021   $51.50   $51.50   $51.50  
  Purchase #2 $174.99   11.292%   $194.7499   $194.75   $194.75   $194.70  
  Purchase #3 $91.89   13.867%   $104.6324   $104.63   $104.65   $104.60  
  Purchase #4 $148.46   5.554%   $156.7055   $156.71   $156.70   $156.70  
  Purchase #5 $197.95   6.584%   $210.983   $210.98   $211.00   $211.00  
  Purchase #6 $138.34   10.132%   $152.3566   $152.36   $152.35   $152.40  
  Purchase #7 $174.93   13.232%   $198.0767   $198.08   $198.10   $198.10  
  7 purchase totals = $974.51       $1,069.0062   $1,069.01   $1,069.05   $1,069.00