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 $238.63   13.568%   $271.0073   $271.01   $271.00   $271.00  
  Purchase #2 $214.79   11.728%   $239.9806   $239.98   $240.00   $240.00  
  Purchase #3 $130.35   11.216%   $144.9701   $144.97   $144.95   $145.00  
  Purchase #4 $73.25   6.374%   $77.919   $77.92   $77.90   $77.90  
  Purchase #5 $55.41   12.850%   $62.5302   $62.53   $62.55   $62.50  
  Purchase #6 $45.96   10.245%   $50.6686   $50.67   $50.65   $50.70  
  Purchase #7 $174.69   12.864%   $197.1621   $197.16   $197.15   $197.20  
  7 purchase totals = $933.08       $1,044.2379   $1,044.24   $1,044.20   $1,044.30