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 $110.58   8.356%   $119.8201   $119.82   $119.80   $119.80  
  Purchase #2 $76.29   6.109%   $80.9506   $80.95   $80.95   $81.00  
  Purchase #3 $43.28   9.306%   $47.3076   $47.31   $47.30   $47.30  
  Purchase #4 $98.62   4.331%   $102.8912   $102.89   $102.90   $102.90  
  Purchase #5 $107.83   5.771%   $114.0529   $114.05   $114.05   $114.10  
  Purchase #6 $106.89   5.777%   $113.065   $113.07   $113.05   $113.10  
  Purchase #7 $12.52   11.355%   $13.9416   $13.94   $13.95   $13.90  
  7 purchase totals = $556.01       $592.0290   $592.03   $592.00   $592.10