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 $82.31   12.428%   $92.5395   $92.54   $92.55   $92.50  
  Purchase #2 $136.90   8.825%   $148.9814   $148.98   $149.00   $149.00  
  Purchase #3 $157.32   9.233%   $171.8454   $171.85   $171.85   $171.80  
  Purchase #4 $166.48   5.439%   $175.5348   $175.53   $175.55   $175.50  
  Purchase #5 $91.70   3.814%   $95.1974   $95.20   $95.20   $95.20  
  Purchase #6 $248.47   8.262%   $268.9986   $269.00   $269.00   $269.00  
  Purchase #7 $22.60   5.234%   $23.7829   $23.78   $23.80   $23.80  
  7 purchase totals = $905.78       $976.8800   $976.88   $976.95   $976.80