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 $32.77   9.796%   $35.9801   $35.98   $36.00   $36.00  
  Purchase #2 $121.66   9.562%   $133.2931   $133.29   $133.30   $133.30  
  Purchase #3 $218.36   10.839%   $242.028   $242.03   $242.05   $242.00  
  Purchase #4 $220.82   9.157%   $241.0405   $241.04   $241.05   $241.00  
  Purchase #5 $118.50   9.421%   $129.6639   $129.66   $129.65   $129.70  
  Purchase #6 $103.93   7.144%   $111.3548   $111.35   $111.35   $111.40  
  Purchase #7 $98.99   3.615%   $102.5685   $102.57   $102.55   $102.60  
  7 purchase totals = $915.03       $995.9289   $995.92   $995.95   $996.00