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 $181.60   12.655%   $204.5815   $204.58   $204.60   $204.60  
  Purchase #2 $133.39   7.348%   $143.1915   $143.19   $143.20   $143.20  
  Purchase #3 $146.34   7.469%   $157.2701   $157.27   $157.25   $157.30  
  Purchase #4 $37.98   8.171%   $41.0833   $41.08   $41.10   $41.10  
  Purchase #5 $206.86   12.766%   $233.2677   $233.27   $233.25   $233.30  
  Purchase #6 $69.84   5.541%   $73.7098   $73.71   $73.70   $73.70  
  Purchase #7 $157.25   7.314%   $168.7513   $168.75   $168.75   $168.80  
  7 purchase totals = $933.26       $1,021.8552   $1,021.85   $1,021.85   $1,022.00