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 $239.77   12.615%   $270.017   $270.02   $270.00   $270.00  
  Purchase #2 $62.96   3.319%   $65.0496   $65.05   $65.05   $65.00  
  Purchase #3 $19.26   3.430%   $19.9206   $19.92   $19.90   $19.90  
  Purchase #4 $220.44   4.129%   $229.542   $229.54   $229.55   $229.50  
  Purchase #5 $223.72   8.207%   $242.0807   $242.08   $242.10   $242.10  
  Purchase #6 $246.75   7.424%   $265.0687   $265.07   $265.05   $265.10  
  Purchase #7 $155.64   3.376%   $160.8944   $160.89   $160.90   $160.90  
  7 purchase totals = $1,168.54       $1,252.5730   $1,252.57   $1,252.55   $1,252.50