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 $34.95   6.664%   $37.2791   $37.28   $37.30   $37.30  
  Purchase #2 $227.33   10.332%   $250.8177   $250.82   $250.80   $250.80  
  Purchase #3 $156.49   11.309%   $174.1875   $174.19   $174.20   $174.20  
  Purchase #4 $56.47   3.809%   $58.6209   $58.62   $58.60   $58.60  
  Purchase #5 $49.69   10.818%   $55.0655   $55.07   $55.05   $55.10  
  Purchase #6 $103.69   11.823%   $115.9493   $115.95   $115.95   $115.90  
  Purchase #7 $163.50   10.423%   $180.5416   $180.54   $180.55   $180.50  
  7 purchase totals = $792.12       $872.4616   $872.47   $872.45   $872.40