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 $200.98   5.409%   $211.851   $211.85   $211.85   $211.90  
  Purchase #2 $148.38   4.110%   $154.4784   $154.48   $154.50   $154.50  
  Purchase #3 $69.43   9.553%   $76.0626   $76.06   $76.05   $76.10  
  Purchase #4 $7.29   12.431%   $8.1962   $8.20   $8.20   $8.20  
  Purchase #5 $76.42   9.522%   $83.6967   $83.70   $83.70   $83.70  
  Purchase #6 $225.72   6.361%   $240.078   $240.08   $240.10   $240.10  
  Purchase #7 $41.29   5.334%   $43.4924   $43.49   $43.50   $43.50  
  7 purchase totals = $769.51       $817.8553   $817.86   $817.90   $818.00