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 $52.87   9.604%   $57.9476   $57.95   $57.95   $57.90  
  Purchase #2 $233.65   13.561%   $265.3353   $265.34   $265.35   $265.30  
  Purchase #3 $225.55   6.423%   $240.0371   $240.04   $240.05   $240.00  
  Purchase #4 $167.67   5.604%   $177.0662   $177.07   $177.05   $177.10  
  Purchase #5 $178.77   12.871%   $201.7795   $201.78   $201.80   $201.80  
  Purchase #6 $151.33   11.620%   $168.9145   $168.91   $168.90   $168.90  
  Purchase #7 $43.35   13.419%   $49.1671   $49.17   $49.15   $49.20  
  7 purchase totals = $1,053.19       $1,160.2473   $1,160.26   $1,160.25   $1,160.20