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 $64.41   8.654%   $69.984   $69.98   $70.00   $70.00  
  Purchase #2 $234.32   7.629%   $252.1963   $252.20   $252.20   $252.20  
  Purchase #3 $99.91   8.368%   $108.2705   $108.27   $108.25   $108.30  
  Purchase #4 $227.99   13.325%   $258.3697   $258.37   $258.35   $258.40  
  Purchase #5 $37.74   6.684%   $40.2625   $40.26   $40.25   $40.30  
  Purchase #6 $200.65   4.121%   $208.9188   $208.92   $208.90   $208.90  
  Purchase #7 $58.84   10.404%   $64.9617   $64.96   $64.95   $65.00  
  7 purchase totals = $923.86       $1,002.9635   $1,002.96   $1,002.90   $1,003.10