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 $174.31   13.128%   $197.1934   $197.19   $197.20   $197.20  
  Purchase #2 $23.91   8.781%   $26.0095   $26.01   $26.00   $26.00  
  Purchase #3 $162.67   8.333%   $176.2253   $176.23   $176.25   $176.20  
  Purchase #4 $34.86   9.512%   $38.1759   $38.18   $38.20   $38.20  
  Purchase #5 $192.94   4.390%   $201.4101   $201.41   $201.40   $201.40  
  Purchase #6 $90.65   9.590%   $99.3433   $99.34   $99.35   $99.30  
  Purchase #7 $173.25   4.614%   $181.2438   $181.24   $181.25   $181.20  
  7 purchase totals = $852.59       $919.6013   $919.60   $919.65   $919.50