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 $61.31   7.585%   $65.9604   $65.96   $65.95   $66.00  
  Purchase #2 $206.86   12.163%   $232.0204   $232.02   $232.00   $232.00  
  Purchase #3 $209.98   12.209%   $235.6165   $235.62   $235.60   $235.60  
  Purchase #4 $215.67   11.268%   $239.9717   $239.97   $239.95   $240.00  
  Purchase #5 $70.30   9.204%   $76.7704   $76.77   $76.75   $76.80  
  Purchase #6 $55.68   5.684%   $58.8449   $58.84   $58.85   $58.80  
  Purchase #7 $127.98   6.248%   $135.9762   $135.98   $136.00   $136.00  
  7 purchase totals = $947.78       $1,045.1605   $1,045.16   $1,045.10   $1,045.20