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 $246.42   11.295%   $274.2531   $274.25   $274.25   $274.30  
  Purchase #2 $100.95   7.512%   $108.5334   $108.53   $108.55   $108.50  
  Purchase #3 $216.30   8.821%   $235.3798   $235.38   $235.40   $235.40  
  Purchase #4 $185.34   11.837%   $207.2787   $207.28   $207.30   $207.30  
  Purchase #5 $102.45   8.372%   $111.0271   $111.03   $111.05   $111.00  
  Purchase #6 $181.42   5.362%   $191.1477   $191.15   $191.15   $191.10  
  Purchase #7 $231.29   3.479%   $239.3366   $239.34   $239.35   $239.30  
  7 purchase totals = $1,264.17       $1,366.9564   $1,366.96   $1,367.05   $1,366.90