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 $70.33   7.459%   $75.5759   $75.58   $75.60   $75.60  
  Purchase #2 $86.53   11.652%   $96.6125   $96.61   $96.60   $96.60  
  Purchase #3 $57.92   3.616%   $60.0144   $60.01   $60.00   $60.00  
  Purchase #4 $119.50   6.704%   $127.5113   $127.51   $127.50   $127.50  
  Purchase #5 $16.40   6.611%   $17.4842   $17.48   $17.50   $17.50  
  Purchase #6 $69.94   11.161%   $77.746   $77.75   $77.75   $77.70  
  Purchase #7 $218.64   11.160%   $243.0402   $243.04   $243.05   $243.00  
  7 purchase totals = $639.26       $697.9845   $697.98   $698.00   $697.90