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 $184.66   13.359%   $209.3287   $209.33   $209.35   $209.30  
  Purchase #2 $204.26   10.415%   $225.5337   $225.53   $225.55   $225.50  
  Purchase #3 $86.35   3.263%   $89.1676   $89.17   $89.15   $89.20  
  Purchase #4 $94.80   8.664%   $103.0135   $103.01   $103.00   $103.00  
  Purchase #5 $202.96   6.497%   $216.1463   $216.15   $216.15   $216.10  
  Purchase #6 $213.82   11.451%   $238.3045   $238.30   $238.30   $238.30  
  Purchase #7 $172.36   12.584%   $194.0498   $194.05   $194.05   $194.00  
  7 purchase totals = $1,159.21       $1,275.5441   $1,275.54   $1,275.55   $1,275.40