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 $35.85   7.631%   $38.5857   $38.59   $38.60   $38.60  
  Purchase #2 $178.79   8.107%   $193.2845   $193.28   $193.30   $193.30  
  Purchase #3 $219.28   8.777%   $238.5262   $238.53   $238.55   $238.50  
  Purchase #4 $39.61   13.455%   $44.9395   $44.94   $44.95   $44.90  
  Purchase #5 $215.85   6.663%   $230.2321   $230.23   $230.25   $230.20  
  Purchase #6 $146.81   13.507%   $166.6396   $166.64   $166.65   $166.60  
  Purchase #7 $45.97   6.828%   $49.1088   $49.11   $49.10   $49.10  
  7 purchase totals = $882.16       $961.3164   $961.32   $961.40   $961.20