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 $61.91   3.424%   $64.0298   $64.03   $64.05   $64.00  
  Purchase #2 $131.62   3.325%   $135.9964   $136.00   $136.00   $136.00  
  Purchase #3 $166.70   9.496%   $182.5298   $182.53   $182.55   $182.50  
  Purchase #4 $217.54   3.738%   $225.6716   $225.67   $225.65   $225.70  
  Purchase #5 $171.31   13.526%   $194.4814   $194.48   $194.50   $194.50  
  Purchase #6 $82.46   6.153%   $87.5338   $87.53   $87.55   $87.50  
  Purchase #7 $106.62   13.764%   $121.2952   $121.30   $121.30   $121.30  
  7 purchase totals = $938.16       $1,011.5380   $1,011.54   $1,011.60   $1,011.50