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 $248.95   10.820%   $275.8864   $275.89   $275.90   $275.90  
  Purchase #2 $141.88   8.790%   $154.3513   $154.35   $154.35   $154.40  
  Purchase #3 $102.88   13.528%   $116.7976   $116.80   $116.80   $116.80  
  Purchase #4 $55.33   4.645%   $57.9001   $57.90   $57.90   $57.90  
  Purchase #5 $66.83   9.749%   $73.3453   $73.35   $73.35   $73.30  
  Purchase #6 $101.71   4.817%   $106.6094   $106.61   $106.60   $106.60  
  Purchase #7 $58.30   7.864%   $62.8847   $62.88   $62.90   $62.90  
  7 purchase totals = $775.88       $847.7748   $847.78   $847.80   $847.80