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   12.648%   $272.1012   $272.10   $272.10   $272.10  
  Purchase #2 $89.97   4.298%   $93.8369   $93.84   $93.85   $93.80  
  Purchase #3 $164.66   5.433%   $173.606   $173.61   $173.60   $173.60  
  Purchase #4 $156.88   10.714%   $173.6881   $173.69   $173.70   $173.70  
  Purchase #5 $241.73   9.865%   $265.5767   $265.58   $265.60   $265.60  
  Purchase #6 $92.70   4.209%   $96.6017   $96.60   $96.60   $96.60  
  Purchase #7 $48.87   7.145%   $52.3618   $52.36   $52.35   $52.40  
  7 purchase totals = $1,036.36       $1,127.7724   $1,127.78   $1,127.80   $1,127.80