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 $239.93   8.363%   $259.9953   $260.00   $260.00   $260.00  
  Purchase #2 $205.68   8.560%   $223.2862   $223.29   $223.30   $223.30  
  Purchase #3 $218.54   13.592%   $248.244   $248.24   $248.25   $248.20  
  Purchase #4 $240.85   11.540%   $268.6441   $268.64   $268.65   $268.60  
  Purchase #5 $191.52   7.106%   $205.1294   $205.13   $205.15   $205.10  
  Purchase #6 $118.87   6.267%   $126.3196   $126.32   $126.30   $126.30  
  Purchase #7 $29.58   12.466%   $33.2674   $33.27   $33.25   $33.30  
  7 purchase totals = $1,244.97       $1,364.8860   $1,364.89   $1,364.90   $1,364.80