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 $87.33   7.209%   $93.6256   $93.63   $93.65   $93.60  
  Purchase #2 $26.87   8.195%   $29.072   $29.07   $29.05   $29.10  
  Purchase #3 $225.32   8.822%   $245.1977   $245.20   $245.20   $245.20  
  Purchase #4 $220.33   12.362%   $247.5672   $247.57   $247.55   $247.60  
  Purchase #5 $158.95   6.576%   $169.4026   $169.40   $169.40   $169.40  
  Purchase #6 $71.90   6.492%   $76.5677   $76.57   $76.55   $76.60  
  Purchase #7 $193.89   5.427%   $204.4124   $204.41   $204.40   $204.40  
  7 purchase totals = $984.59       $1,065.8452   $1,065.85   $1,065.80   $1,065.90