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 $238.95   11.740%   $267.0027   $267.00   $267.00   $267.00  
  Purchase #2 $88.91   5.737%   $94.0108   $94.01   $94.00   $94.00  
  Purchase #3 $183.41   11.211%   $203.9721   $203.97   $203.95   $204.00  
  Purchase #4 $21.80   6.205%   $23.1527   $23.15   $23.15   $23.20  
  Purchase #5 $58.31   6.644%   $62.1841   $62.18   $62.20   $62.20  
  Purchase #6 $28.79   13.325%   $32.6263   $32.63   $32.65   $32.60  
  Purchase #7 $50.27   5.372%   $52.9705   $52.97   $52.95   $53.00  
  7 purchase totals = $670.44       $735.9192   $735.91   $735.90   $736.00