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 $184.39   10.681%   $204.0847   $204.08   $204.10   $204.10  
  Purchase #2 $16.41   13.349%   $18.6006   $18.60   $18.60   $18.60  
  Purchase #3 $53.39   9.204%   $58.304   $58.30   $58.30   $58.30  
  Purchase #4 $17.87   3.749%   $18.5399   $18.54   $18.55   $18.50  
  Purchase #5 $187.66   5.662%   $198.2853   $198.29   $198.30   $198.30  
  Purchase #6 $180.63   5.140%   $189.9144   $189.91   $189.90   $189.90  
  Purchase #7 $167.64   7.713%   $180.5701   $180.57   $180.55   $180.60  
  7 purchase totals = $807.99       $868.2990   $868.29   $868.30   $868.30