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 $188.33   13.746%   $214.2178   $214.22   $214.20   $214.20  
  Purchase #2 $23.95   3.626%   $24.8184   $24.82   $24.80   $24.80  
  Purchase #3 $88.74   3.184%   $91.5655   $91.57   $91.55   $91.60  
  Purchase #4 $250.33   5.265%   $263.5099   $263.51   $263.50   $263.50  
  Purchase #5 $94.72   10.581%   $104.7423   $104.74   $104.75   $104.70  
  Purchase #6 $188.33   11.516%   $210.0181   $210.02   $210.00   $210.00  
  Purchase #7 $240.65   5.322%   $253.4574   $253.46   $253.45   $253.50  
  7 purchase totals = $1,075.05       $1,162.3294   $1,162.34   $1,162.25   $1,162.30