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 $182.75   9.260%   $199.6727   $199.67   $199.65   $199.70  
  Purchase #2 $173.77   4.282%   $181.2108   $181.21   $181.20   $181.20  
  Purchase #3 $166.50   4.358%   $173.7561   $173.76   $173.75   $173.80  
  Purchase #4 $201.31   9.346%   $220.1244   $220.12   $220.10   $220.10  
  Purchase #5 $128.77   6.283%   $136.8606   $136.86   $136.85   $136.90  
  Purchase #6 $233.85   7.226%   $250.748   $250.75   $250.75   $250.70  
  Purchase #7 $157.63   11.162%   $175.2247   $175.22   $175.20   $175.20  
  7 purchase totals = $1,244.58       $1,337.5973   $1,337.59   $1,337.50   $1,337.60