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 $247.93   7.224%   $265.8405   $265.84   $265.85   $265.80  
  Purchase #2 $164.82   11.199%   $183.2782   $183.28   $183.30   $183.30  
  Purchase #3 $58.63   3.459%   $60.658   $60.66   $60.65   $60.70  
  Purchase #4 $83.25   8.814%   $90.5877   $90.59   $90.60   $90.60  
  Purchase #5 $155.28   11.574%   $173.2521   $173.25   $173.25   $173.30  
  Purchase #6 $224.33   8.251%   $242.8395   $242.84   $242.85   $242.80  
  Purchase #7 $44.90   7.350%   $48.2002   $48.20   $48.20   $48.20  
  7 purchase totals = $979.14       $1,064.6562   $1,064.66   $1,064.70   $1,064.70