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 $228.37   12.823%   $257.6539   $257.65   $257.65   $257.70  
  Purchase #2 $173.73   7.174%   $186.1934   $186.19   $186.20   $186.20  
  Purchase #3 $87.98   3.726%   $91.2581   $91.26   $91.25   $91.30  
  Purchase #4 $65.78   3.391%   $68.0106   $68.01   $68.00   $68.00  
  Purchase #5 $155.42   4.405%   $162.2663   $162.27   $162.25   $162.30  
  Purchase #6 $24.93   9.258%   $27.238   $27.24   $27.25   $27.20  
  Purchase #7 $130.26   7.363%   $139.851   $139.85   $139.85   $139.90  
  7 purchase totals = $866.47       $932.4713   $932.47   $932.45   $932.60