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 $61.51   8.300%   $66.6153   $66.62   $66.60   $66.60  
  Purchase #2 $184.68   3.660%   $191.4393   $191.44   $191.45   $191.40  
  Purchase #3 $211.77   9.723%   $232.3604   $232.36   $232.35   $232.40  
  Purchase #4 $152.62   10.825%   $169.1411   $169.14   $169.15   $169.10  
  Purchase #5 $128.25   4.460%   $133.97   $133.97   $133.95   $134.00  
  Purchase #6 $110.70   12.676%   $124.7323   $124.73   $124.75   $124.70  
  Purchase #7 $130.30   8.134%   $140.8986   $140.90   $140.90   $140.90  
  7 purchase totals = $979.83       $1,059.1570   $1,059.16   $1,059.15   $1,059.10