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 $87.77   10.207%   $96.7287   $96.73   $96.75   $96.70  
  Purchase #2 $144.65   12.807%   $163.1753   $163.18   $163.20   $163.20  
  Purchase #3 $249.64   12.573%   $281.0272   $281.03   $281.05   $281.00  
  Purchase #4 $160.61   3.716%   $166.5783   $166.58   $166.60   $166.60  
  Purchase #5 $152.86   13.837%   $174.0112   $174.01   $174.00   $174.00  
  Purchase #6 $59.73   7.147%   $63.9989   $64.00   $64.00   $64.00  
  Purchase #7 $217.28   3.464%   $224.8066   $224.81   $224.80   $224.80  
  7 purchase totals = $1,072.54       $1,170.3262   $1,170.34   $1,170.40   $1,170.30