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 $190.34   5.586%   $200.9724   $200.97   $200.95   $201.00  
  Purchase #2 $59.84   6.202%   $63.5513   $63.55   $63.55   $63.60  
  Purchase #3 $42.27   5.360%   $44.5357   $44.54   $44.55   $44.50  
  Purchase #4 $76.39   4.777%   $80.0392   $80.04   $80.05   $80.00  
  Purchase #5 $102.86   11.161%   $114.3402   $114.34   $114.35   $114.30  
  Purchase #6 $118.32   9.469%   $129.5237   $129.52   $129.50   $129.50  
  Purchase #7 $62.77   5.687%   $66.3397   $66.34   $66.35   $66.30  
  7 purchase totals = $652.79       $699.3022   $699.30   $699.30   $699.20