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 $85.34   3.515%   $88.3397   $88.34   $88.35   $88.30  
  Purchase #2 $208.53   11.154%   $231.7894   $231.79   $231.80   $231.80  
  Purchase #3 $68.39   3.199%   $70.5778   $70.58   $70.60   $70.60  
  Purchase #4 $107.67   8.599%   $116.9285   $116.93   $116.95   $116.90  
  Purchase #5 $38.97   7.326%   $41.8249   $41.82   $41.80   $41.80  
  Purchase #6 $227.27   8.246%   $246.0107   $246.01   $246.00   $246.00  
  Purchase #7 $95.95   5.531%   $101.257   $101.26   $101.25   $101.30  
  7 purchase totals = $832.12       $896.7280   $896.73   $896.75   $896.70