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 $86.42   11.270%   $96.1595   $96.16   $96.15   $96.20  
  Purchase #2 $68.40   5.424%   $72.11   $72.11   $72.10   $72.10  
  Purchase #3 $215.62   7.550%   $231.8993   $231.90   $231.90   $231.90  
  Purchase #4 $247.90   7.771%   $267.1643   $267.16   $267.15   $267.20  
  Purchase #5 $60.66   7.379%   $65.1361   $65.14   $65.15   $65.10  
  Purchase #6 $41.29   4.394%   $43.1043   $43.10   $43.10   $43.10  
  Purchase #7 $124.35   11.303%   $138.4053   $138.41   $138.40   $138.40  
  7 purchase totals = $844.64       $913.9788   $913.98   $913.95   $914.00