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 $239.98   11.559%   $267.7193   $267.72   $267.70   $267.70  
  Purchase #2 $212.90   5.661%   $224.9523   $224.95   $224.95   $225.00  
  Purchase #3 $179.48   6.834%   $191.7457   $191.75   $191.75   $191.70  
  Purchase #4 $29.58   13.245%   $33.4979   $33.50   $33.50   $33.50  
  Purchase #5 $133.95   10.317%   $147.7696   $147.77   $147.75   $147.80  
  Purchase #6 $205.29   9.298%   $224.3779   $224.38   $224.40   $224.40  
  Purchase #7 $113.81   9.476%   $124.5946   $124.59   $124.60   $124.60  
  7 purchase totals = $1,114.99       $1,214.6573   $1,214.66   $1,214.65   $1,214.70