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 $250.57   10.280%   $276.3286   $276.33   $276.35   $276.30  
  Purchase #2 $151.49   11.526%   $168.9507   $168.95   $168.95   $169.00  
  Purchase #3 $243.63   4.205%   $253.8746   $253.87   $253.85   $253.90  
  Purchase #4 $70.85   5.760%   $74.931   $74.93   $74.95   $74.90  
  Purchase #5 $230.76   7.217%   $247.4139   $247.41   $247.40   $247.40  
  Purchase #6 $162.74   3.827%   $168.9681   $168.97   $168.95   $169.00  
  Purchase #7 $184.48   5.696%   $194.988   $194.99   $195.00   $195.00  
  7 purchase totals = $1,294.52       $1,385.4549   $1,385.45   $1,385.45   $1,385.50