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 $221.31   11.646%   $247.0838   $247.08   $247.10   $247.10  
  Purchase #2 $187.95   4.207%   $195.8571   $195.86   $195.85   $195.90  
  Purchase #3 $79.33   9.858%   $87.1504   $87.15   $87.15   $87.20  
  Purchase #4 $73.89   8.246%   $79.983   $79.98   $80.00   $80.00  
  Purchase #5 $30.83   4.772%   $32.3012   $32.30   $32.30   $32.30  
  Purchase #6 $172.63   8.370%   $187.0791   $187.08   $187.10   $187.10  
  Purchase #7 $84.25   12.767%   $95.0062   $95.01   $95.00   $95.00  
  7 purchase totals = $850.19       $924.4608   $924.46   $924.50   $924.60