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 $88.48   11.503%   $98.6579   $98.66   $98.65   $98.70  
  Purchase #2 $21.75   6.753%   $23.2188   $23.22   $23.20   $23.20  
  Purchase #3 $249.34   5.869%   $263.9738   $263.97   $263.95   $264.00  
  Purchase #4 $220.69   9.587%   $241.8476   $241.85   $241.85   $241.80  
  Purchase #5 $172.76   4.685%   $180.8538   $180.85   $180.85   $180.90  
  Purchase #6 $14.59   9.614%   $15.9927   $15.99   $16.00   $16.00  
  Purchase #7 $40.87   5.304%   $43.0377   $43.04   $43.05   $43.00  
  7 purchase totals = $808.48       $867.5823   $867.58   $867.55   $867.60