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 $185.62   10.459%   $205.034   $205.03   $205.05   $205.00  
  Purchase #2 $141.43   4.390%   $147.6388   $147.64   $147.65   $147.60  
  Purchase #3 $60.63   7.366%   $65.096   $65.10   $65.10   $65.10  
  Purchase #4 $141.85   6.826%   $151.5327   $151.53   $151.55   $151.50  
  Purchase #5 $50.84   12.647%   $57.2697   $57.27   $57.25   $57.30  
  Purchase #6 $92.66   4.400%   $96.737   $96.74   $96.75   $96.70  
  Purchase #7 $118.46   9.255%   $129.4235   $129.42   $129.40   $129.40  
  7 purchase totals = $791.49       $852.7317   $852.73   $852.75   $852.60