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 $241.98   10.643%   $267.7339   $267.73   $267.75   $267.70  
  Purchase #2 $156.98   9.207%   $171.4331   $171.43   $171.45   $171.40  
  Purchase #3 $205.78   12.772%   $232.0622   $232.06   $232.05   $232.10  
  Purchase #4 $193.62   6.351%   $205.9168   $205.92   $205.90   $205.90  
  Purchase #5 $177.70   5.198%   $186.9368   $186.94   $186.95   $186.90  
  Purchase #6 $230.67   4.874%   $241.9129   $241.91   $241.90   $241.90  
  Purchase #7 $86.97   10.139%   $95.7879   $95.79   $95.80   $95.80  
  7 purchase totals = $1,293.70       $1,401.7836   $1,401.78   $1,401.80   $1,401.70