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 $53.72   11.432%   $59.8613   $59.86   $59.85   $59.90  
  Purchase #2 $44.36   12.368%   $49.8464   $49.85   $49.85   $49.80  
  Purchase #3 $220.27   11.296%   $245.1517   $245.15   $245.15   $245.20  
  Purchase #4 $132.25   11.506%   $147.4667   $147.47   $147.45   $147.50  
  Purchase #5 $226.51   3.733%   $234.9656   $234.97   $234.95   $235.00  
  Purchase #6 $213.30   4.662%   $223.244   $223.24   $223.25   $223.20  
  Purchase #7 $31.85   10.584%   $35.221   $35.22   $35.20   $35.20  
  7 purchase totals = $922.26       $995.7567   $995.76   $995.70   $995.80