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 $33.76   6.526%   $35.9632   $35.96   $35.95   $36.00  
  Purchase #2 $214.74   12.308%   $241.1702   $241.17   $241.15   $241.20  
  Purchase #3 $246.90   8.818%   $268.6716   $268.67   $268.65   $268.70  
  Purchase #4 $239.26   4.635%   $250.3497   $250.35   $250.35   $250.30  
  Purchase #5 $80.98   11.785%   $90.5235   $90.52   $90.50   $90.50  
  Purchase #6 $139.79   4.183%   $145.6374   $145.64   $145.65   $145.60  
  Purchase #7 $161.81   9.624%   $177.3826   $177.38   $177.40   $177.40  
  7 purchase totals = $1,117.24       $1,209.6982   $1,209.69   $1,209.65   $1,209.70