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 $108.58   7.626%   $116.8603   $116.86   $116.85   $116.90  
  Purchase #2 $204.67   12.680%   $230.6222   $230.62   $230.60   $230.60  
  Purchase #3 $180.72   5.671%   $190.9686   $190.97   $190.95   $191.00  
  Purchase #4 $87.80   12.622%   $98.8821   $98.88   $98.90   $98.90  
  Purchase #5 $149.91   3.383%   $154.9815   $154.98   $155.00   $155.00  
  Purchase #6 $165.78   12.407%   $186.3483   $186.35   $186.35   $186.30  
  Purchase #7 $65.90   9.265%   $72.0056   $72.01   $72.00   $72.00  
  7 purchase totals = $963.36       $1,050.6686   $1,050.67   $1,050.65   $1,050.70