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 $232.31   9.272%   $253.8498   $253.85   $253.85   $253.80  
  Purchase #2 $167.97   4.289%   $175.1742   $175.17   $175.15   $175.20  
  Purchase #3 $85.39   8.339%   $92.5107   $92.51   $92.50   $92.50  
  Purchase #4 $80.65   7.812%   $86.9504   $86.95   $86.95   $87.00  
  Purchase #5 $49.90   10.498%   $55.1385   $55.14   $55.15   $55.10  
  Purchase #6 $241.85   5.154%   $254.3149   $254.31   $254.30   $254.30  
  Purchase #7 $51.62   5.637%   $54.5298   $54.53   $54.55   $54.50  
  7 purchase totals = $909.69       $972.4683   $972.46   $972.45   $972.40