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 $194.30   6.198%   $206.3427   $206.34   $206.35   $206.30  
  Purchase #2 $91.77   3.310%   $94.8076   $94.81   $94.80   $94.80  
  Purchase #3 $191.52   3.865%   $198.9222   $198.92   $198.90   $198.90  
  Purchase #4 $87.96   7.599%   $94.6441   $94.64   $94.65   $94.60  
  Purchase #5 $67.57   12.320%   $75.8946   $75.89   $75.90   $75.90  
  Purchase #6 $80.82   13.785%   $91.961   $91.96   $91.95   $92.00  
  Purchase #7 $76.39   9.458%   $83.615   $83.62   $83.60   $83.60  
  7 purchase totals = $790.33       $846.1872   $846.18   $846.15   $846.10