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 $245.53   8.142%   $265.5211   $265.52   $265.50   $265.50  
  Purchase #2 $158.99   11.413%   $177.1355   $177.14   $177.15   $177.10  
  Purchase #3 $119.90   13.873%   $136.5337   $136.53   $136.55   $136.50  
  Purchase #4 $194.35   12.821%   $219.2676   $219.27   $219.25   $219.30  
  Purchase #5 $54.44   13.319%   $61.6909   $61.69   $61.70   $61.70  
  Purchase #6 $67.91   5.309%   $71.5153   $71.52   $71.50   $71.50  
  Purchase #7 $128.83   10.222%   $141.999   $142.00   $142.00   $142.00  
  7 purchase totals = $969.95       $1,073.6631   $1,073.67   $1,073.65   $1,073.60