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 $37.62   13.260%   $42.6084   $42.61   $42.60   $42.60  
  Purchase #2 $94.72   3.483%   $98.0191   $98.02   $98.00   $98.00  
  Purchase #3 $153.52   5.817%   $162.4503   $162.45   $162.45   $162.50  
  Purchase #4 $229.38   13.331%   $259.9586   $259.96   $259.95   $260.00  
  Purchase #5 $202.99   13.192%   $229.7684   $229.77   $229.75   $229.80  
  Purchase #6 $173.81   12.274%   $195.1434   $195.14   $195.15   $195.10  
  Purchase #7 $152.97   8.185%   $165.4906   $165.49   $165.50   $165.50  
  7 purchase totals = $1,045.01       $1,153.4388   $1,153.44   $1,153.40   $1,153.50