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 $7.99   4.590%   $8.3567   $8.36   $8.35   $8.40  
  Purchase #2 $162.76   3.695%   $168.774   $168.77   $168.75   $168.80  
  Purchase #3 $19.85   5.582%   $20.958   $20.96   $20.95   $21.00  
  Purchase #4 $148.48   11.239%   $165.1677   $165.17   $165.15   $165.20  
  Purchase #5 $239.50   4.524%   $250.335   $250.34   $250.35   $250.30  
  Purchase #6 $77.34   7.713%   $83.3052   $83.31   $83.30   $83.30  
  Purchase #7 $209.69   8.772%   $228.084   $228.08   $228.10   $228.10  
  7 purchase totals = $865.61       $924.9806   $924.99   $924.95   $925.10