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 $84.82   13.559%   $96.3207   $96.32   $96.30   $96.30  
  Purchase #2 $150.32   7.600%   $161.7443   $161.74   $161.75   $161.70  
  Purchase #3 $99.66   12.137%   $111.7557   $111.76   $111.75   $111.80  
  Purchase #4 $129.36   5.665%   $136.6882   $136.69   $136.70   $136.70  
  Purchase #5 $213.77   10.133%   $235.4313   $235.43   $235.45   $235.40  
  Purchase #6 $201.90   8.653%   $219.3704   $219.37   $219.35   $219.40  
  Purchase #7 $68.51   9.704%   $75.1582   $75.16   $75.15   $75.20  
  7 purchase totals = $948.34       $1,036.4688   $1,036.47   $1,036.45   $1,036.50