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 $210.44   8.819%   $228.9987   $229.00   $229.00   $229.00  
  Purchase #2 $241.93   10.299%   $266.8464   $266.85   $266.85   $266.80  
  Purchase #3 $42.35   12.372%   $47.5895   $47.59   $47.60   $47.60  
  Purchase #4 $50.97   4.394%   $53.2096   $53.21   $53.20   $53.20  
  Purchase #5 $31.48   5.216%   $33.122   $33.12   $33.10   $33.10  
  Purchase #6 $53.81   6.805%   $57.4718   $57.47   $57.45   $57.50  
  Purchase #7 $91.75   5.343%   $96.6522   $96.65   $96.65   $96.70  
  7 purchase totals = $722.73       $783.8902   $783.89   $783.85   $783.90