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 $113.99   7.578%   $122.6282   $122.63   $122.65   $122.60  
  Purchase #2 $147.95   7.441%   $158.959   $158.96   $158.95   $159.00  
  Purchase #3 $55.85   8.369%   $60.5241   $60.52   $60.50   $60.50  
  Purchase #4 $250.63   7.270%   $268.8508   $268.85   $268.85   $268.90  
  Purchase #5 $206.75   7.163%   $221.5595   $221.56   $221.55   $221.60  
  Purchase #6 $122.61   10.439%   $135.4093   $135.41   $135.40   $135.40  
  Purchase #7 $237.86   8.607%   $258.3326   $258.33   $258.35   $258.30  
  7 purchase totals = $1,135.64       $1,226.2635   $1,226.26   $1,226.25   $1,226.30