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 $208.61   5.629%   $220.3527   $220.35   $220.35   $220.40  
  Purchase #2 $46.51   3.317%   $48.0527   $48.05   $48.05   $48.10  
  Purchase #3 $54.51   4.872%   $57.1657   $57.17   $57.15   $57.20  
  Purchase #4 $159.29   6.844%   $170.1918   $170.19   $170.20   $170.20  
  Purchase #5 $207.35   10.210%   $228.5204   $228.52   $228.50   $228.50  
  Purchase #6 $133.62   13.444%   $151.5839   $151.58   $151.60   $151.60  
  Purchase #7 $211.89   12.846%   $239.1094   $239.11   $239.10   $239.10  
  7 purchase totals = $1,021.78       $1,114.9766   $1,114.97   $1,114.95   $1,115.10