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 $67.34   11.629%   $75.171   $75.17   $75.15   $75.20  
  Purchase #2 $181.75   3.527%   $188.1603   $188.16   $188.15   $188.20  
  Purchase #3 $166.97   5.187%   $175.6307   $175.63   $175.65   $175.60  
  Purchase #4 $207.90   10.653%   $230.0476   $230.05   $230.05   $230.00  
  Purchase #5 $248.76   13.708%   $282.86   $282.86   $282.85   $282.90  
  Purchase #6 $234.61   7.454%   $252.0978   $252.10   $252.10   $252.10  
  Purchase #7 $115.52   4.344%   $120.5382   $120.54   $120.55   $120.50  
  7 purchase totals = $1,222.85       $1,324.5056   $1,324.51   $1,324.50   $1,324.50