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 $45.92   5.825%   $48.5948   $48.59   $48.60   $48.60  
  Purchase #2 $157.85   12.327%   $177.3082   $177.31   $177.30   $177.30  
  Purchase #3 $47.95   10.236%   $52.8582   $52.86   $52.85   $52.90  
  Purchase #4 $5.47   10.173%   $6.0265   $6.03   $6.05   $6.00  
  Purchase #5 $71.64   5.427%   $75.5279   $75.53   $75.55   $75.50  
  Purchase #6 $116.51   11.440%   $129.8387   $129.84   $129.85   $129.80  
  Purchase #7 $206.39   9.767%   $226.5481   $226.55   $226.55   $226.50  
  7 purchase totals = $651.73       $716.7024   $716.71   $716.75   $716.60