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 $47.48   9.798%   $52.1321   $52.13   $52.15   $52.10  
  Purchase #2 $232.92   3.215%   $240.4084   $240.41   $240.40   $240.40  
  Purchase #3 $46.98   3.851%   $48.7892   $48.79   $48.80   $48.80  
  Purchase #4 $243.91   4.848%   $255.7348   $255.73   $255.75   $255.70  
  Purchase #5 $177.55   11.452%   $197.883   $197.88   $197.90   $197.90  
  Purchase #6 $247.68   7.257%   $265.6541   $265.65   $265.65   $265.70  
  Purchase #7 $126.82   7.529%   $136.3683   $136.37   $136.35   $136.40  
  7 purchase totals = $1,123.34       $1,196.9699   $1,196.96   $1,197.00   $1,197.00