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 $182.43   13.470%   $207.0033   $207.00   $207.00   $207.00  
  Purchase #2 $82.56   5.804%   $87.3518   $87.35   $87.35   $87.40  
  Purchase #3 $121.62   11.311%   $135.3764   $135.38   $135.40   $135.40  
  Purchase #4 $222.73   12.454%   $250.4688   $250.47   $250.45   $250.50  
  Purchase #5 $163.33   6.514%   $173.9693   $173.97   $173.95   $174.00  
  Purchase #6 $37.95   7.260%   $40.7052   $40.71   $40.70   $40.70  
  Purchase #7 $113.86   4.202%   $118.6444   $118.64   $118.65   $118.60  
  7 purchase totals = $924.48       $1,013.5192   $1,013.52   $1,013.50   $1,013.60