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 $211.39   5.446%   $222.9023   $222.90   $222.90   $222.90  
  Purchase #2 $104.26   11.116%   $115.8495   $115.85   $115.85   $115.80  
  Purchase #3 $54.50   10.282%   $60.1037   $60.10   $60.10   $60.10  
  Purchase #4 $31.62   13.270%   $35.816   $35.82   $35.80   $35.80  
  Purchase #5 $71.49   5.673%   $75.5456   $75.55   $75.55   $75.50  
  Purchase #6 $109.97   9.302%   $120.1994   $120.20   $120.20   $120.20  
  Purchase #7 $127.47   3.286%   $131.6587   $131.66   $131.65   $131.70  
  7 purchase totals = $710.70       $762.0752   $762.08   $762.05   $762.00