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 $241.55   11.862%   $270.2027   $270.20   $270.20   $270.20  
  Purchase #2 $197.77   10.276%   $218.0928   $218.09   $218.10   $218.10  
  Purchase #3 $29.49   5.463%   $31.101   $31.10   $31.10   $31.10  
  Purchase #4 $192.61   11.361%   $214.4924   $214.49   $214.50   $214.50  
  Purchase #5 $169.53   11.602%   $189.1989   $189.20   $189.20   $189.20  
  Purchase #6 $219.89   10.527%   $243.0378   $243.04   $243.05   $243.00  
  Purchase #7 $96.58   5.172%   $101.5751   $101.58   $101.60   $101.60  
  7 purchase totals = $1,147.42       $1,267.7007   $1,267.70   $1,267.75   $1,267.70