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 $234.27   7.612%   $252.1026   $252.10   $252.10   $252.10  
  Purchase #2 $170.51   3.199%   $175.9646   $175.96   $175.95   $176.00  
  Purchase #3 $62.25   3.852%   $64.6479   $64.65   $64.65   $64.60  
  Purchase #4 $75.64   13.753%   $86.0428   $86.04   $86.05   $86.00  
  Purchase #5 $166.92   13.454%   $189.3774   $189.38   $189.40   $189.40  
  Purchase #6 $79.58   9.264%   $86.9523   $86.95   $86.95   $87.00  
  Purchase #7 $40.66   9.249%   $44.4206   $44.42   $44.40   $44.40  
  7 purchase totals = $829.83       $899.5082   $899.50   $899.50   $899.50