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 $82.57   12.312%   $92.736   $92.74   $92.75   $92.70  
  Purchase #2 $22.36   3.135%   $23.061   $23.06   $23.05   $23.10  
  Purchase #3 $183.80   8.865%   $200.0939   $200.09   $200.10   $200.10  
  Purchase #4 $31.67   13.233%   $35.8609   $35.86   $35.85   $35.90  
  Purchase #5 $138.92   7.461%   $149.2848   $149.28   $149.30   $149.30  
  Purchase #6 $194.51   13.309%   $220.3973   $220.40   $220.40   $220.40  
  Purchase #7 $131.82   5.373%   $138.9027   $138.90   $138.90   $138.90  
  7 purchase totals = $785.65       $860.3366   $860.33   $860.35   $860.40