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 $136.74   4.662%   $143.1148   $143.11   $143.10   $143.10  
  Purchase #2 $76.75   12.727%   $86.518   $86.52   $86.50   $86.50  
  Purchase #3 $56.65   7.816%   $61.0778   $61.08   $61.10   $61.10  
  Purchase #4 $221.37   3.297%   $228.6686   $228.67   $228.65   $228.70  
  Purchase #5 $34.36   13.655%   $39.0519   $39.05   $39.05   $39.10  
  Purchase #6 $49.27   4.579%   $51.5261   $51.53   $51.55   $51.50  
  Purchase #7 $46.45   10.735%   $51.4364   $51.44   $51.45   $51.40  
  7 purchase totals = $621.59       $661.3936   $661.40   $661.40   $661.40