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 $243.35   10.118%   $267.9722   $267.97   $267.95   $268.00  
  Purchase #2 $182.71   12.160%   $204.9275   $204.93   $204.95   $204.90  
  Purchase #3 $247.37   10.206%   $272.6166   $272.62   $272.60   $272.60  
  Purchase #4 $85.79   9.434%   $93.8834   $93.88   $93.90   $93.90  
  Purchase #5 $117.97   7.277%   $126.5547   $126.55   $126.55   $126.60  
  Purchase #6 $39.70   9.285%   $43.3861   $43.39   $43.40   $43.40  
  Purchase #7 $140.81   3.401%   $145.5989   $145.60   $145.60   $145.60  
  7 purchase totals = $1,057.70       $1,154.9394   $1,154.94   $1,154.95   $1,155.00