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 $107.84   9.428%   $118.0072   $118.01   $118.00   $118.00  
  Purchase #2 $189.33   8.260%   $204.9687   $204.97   $204.95   $205.00  
  Purchase #3 $82.91   8.326%   $89.8131   $89.81   $89.80   $89.80  
  Purchase #4 $127.67   6.476%   $135.9379   $135.94   $135.95   $135.90  
  Purchase #5 $112.53   5.823%   $119.0826   $119.08   $119.10   $119.10  
  Purchase #6 $36.91   10.243%   $40.6907   $40.69   $40.70   $40.70  
  Purchase #7 $118.62   6.794%   $126.679   $126.68   $126.70   $126.70  
  7 purchase totals = $775.81       $835.1792   $835.18   $835.20   $835.20