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 $186.74   6.174%   $198.2693   $198.27   $198.25   $198.30  
  Purchase #2 $62.37   10.333%   $68.8147   $68.81   $68.80   $68.80  
  Purchase #3 $154.44   3.251%   $159.4608   $159.46   $159.45   $159.50  
  Purchase #4 $177.59   12.195%   $199.2471   $199.25   $199.25   $199.20  
  Purchase #5 $90.65   4.406%   $94.644   $94.64   $94.65   $94.60  
  Purchase #6 $94.62   12.431%   $106.3822   $106.38   $106.40   $106.40  
  Purchase #7 $190.51   6.743%   $203.3561   $203.36   $203.35   $203.40  
  7 purchase totals = $956.92       $1,030.1742   $1,030.17   $1,030.15   $1,030.20