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 $244.71   13.272%   $277.1879   $277.19   $277.20   $277.20  
  Purchase #2 $163.97   7.859%   $176.8564   $176.86   $176.85   $176.90  
  Purchase #3 $62.46   11.759%   $69.8047   $69.80   $69.80   $69.80  
  Purchase #4 $218.28   9.422%   $238.8463   $238.85   $238.85   $238.80  
  Purchase #5 $35.38   11.130%   $39.3178   $39.32   $39.30   $39.30  
  Purchase #6 $49.82   5.579%   $52.5995   $52.60   $52.60   $52.60  
  Purchase #7 $179.89   10.150%   $198.1488   $198.15   $198.15   $198.10  
  7 purchase totals = $954.51       $1,052.7614   $1,052.77   $1,052.75   $1,052.70