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 $84.48   10.590%   $93.4264   $93.43   $93.45   $93.40  
  Purchase #2 $139.89   9.330%   $152.9417   $152.94   $152.95   $152.90  
  Purchase #3 $87.90   9.869%   $96.5749   $96.57   $96.55   $96.60  
  Purchase #4 $185.39   6.633%   $197.6869   $197.69   $197.70   $197.70  
  Purchase #5 $64.71   6.797%   $69.1083   $69.11   $69.10   $69.10  
  Purchase #6 $204.25   13.523%   $231.8707   $231.87   $231.85   $231.90  
  Purchase #7 $133.81   6.585%   $142.6214   $142.62   $142.60   $142.60  
  7 purchase totals = $900.43       $984.2303   $984.23   $984.20   $984.20