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 $91.67   7.502%   $98.5471   $98.55   $98.55   $98.50  
  Purchase #2 $96.79   11.290%   $107.7176   $107.72   $107.70   $107.70  
  Purchase #3 $23.33   4.726%   $24.4326   $24.43   $24.45   $24.40  
  Purchase #4 $34.66   4.541%   $36.2339   $36.23   $36.25   $36.20  
  Purchase #5 $210.89   4.840%   $221.0971   $221.10   $221.10   $221.10  
  Purchase #6 $22.87   7.777%   $24.6486   $24.65   $24.65   $24.60  
  Purchase #7 $220.27   8.300%   $238.5524   $238.55   $238.55   $238.60  
  7 purchase totals = $700.48       $751.2293   $751.23   $751.25   $751.10