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 $82.34   10.831%   $91.2582   $91.26   $91.25   $91.30  
  Purchase #2 $96.76   7.824%   $104.3305   $104.33   $104.35   $104.30  
  Purchase #3 $71.25   5.332%   $75.0491   $75.05   $75.05   $75.00  
  Purchase #4 $200.61   6.767%   $214.1853   $214.19   $214.20   $214.20  
  Purchase #5 $91.85   5.415%   $96.8237   $96.82   $96.80   $96.80  
  Purchase #6 $176.94   8.485%   $191.9534   $191.95   $191.95   $192.00  
  Purchase #7 $183.85   8.758%   $199.9516   $199.95   $199.95   $200.00  
  7 purchase totals = $903.60       $973.5518   $973.55   $973.55   $973.60