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 $143.38   8.168%   $155.0913   $155.09   $155.10   $155.10  
  Purchase #2 $73.96   4.372%   $77.1935   $77.19   $77.20   $77.20  
  Purchase #3 $57.39   6.320%   $61.017   $61.02   $61.00   $61.00  
  Purchase #4 $6.64   8.624%   $7.2126   $7.21   $7.20   $7.20  
  Purchase #5 $41.41   6.454%   $44.0826   $44.08   $44.10   $44.10  
  Purchase #6 $163.25   7.557%   $175.5868   $175.59   $175.60   $175.60  
  Purchase #7 $6.45   7.669%   $6.9447   $6.94   $6.95   $6.90  
  7 purchase totals = $492.48       $527.1285   $527.12   $527.15   $527.10