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 $74.79   6.562%   $79.6977   $79.70   $79.70   $79.70  
  Purchase #2 $205.33   11.354%   $228.6432   $228.64   $228.65   $228.60  
  Purchase #3 $92.83   9.154%   $101.3277   $101.33   $101.35   $101.30  
  Purchase #4 $242.63   13.821%   $276.1639   $276.16   $276.15   $276.20  
  Purchase #5 $225.79   3.288%   $233.214   $233.21   $233.20   $233.20  
  Purchase #6 $52.26   11.339%   $58.1858   $58.19   $58.20   $58.20  
  Purchase #7 $26.58   11.433%   $29.6189   $29.62   $29.60   $29.60  
  7 purchase totals = $920.21       $1,006.8512   $1,006.85   $1,006.85   $1,006.80