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 $54.92   10.842%   $60.8744   $60.87   $60.85   $60.90  
  Purchase #2 $126.66   11.198%   $140.8434   $140.84   $140.85   $140.80  
  Purchase #3 $41.41   11.761%   $46.2802   $46.28   $46.30   $46.30  
  Purchase #4 $217.50   4.239%   $226.7198   $226.72   $226.70   $226.70  
  Purchase #5 $79.47   11.314%   $88.4612   $88.46   $88.45   $88.50  
  Purchase #6 $174.66   5.146%   $183.648   $183.65   $183.65   $183.60  
  Purchase #7 $185.49   12.550%   $208.769   $208.77   $208.75   $208.80  
  7 purchase totals = $880.11       $955.5960   $955.59   $955.55   $955.60