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 $239.66   11.690%   $267.6763   $267.68   $267.70   $267.70  
  Purchase #2 $126.68   6.774%   $135.2613   $135.26   $135.25   $135.30  
  Purchase #3 $171.43   10.430%   $189.3101   $189.31   $189.30   $189.30  
  Purchase #4 $171.76   5.628%   $181.4267   $181.43   $181.45   $181.40  
  Purchase #5 $85.97   6.696%   $91.7266   $91.73   $91.75   $91.70  
  Purchase #6 $178.78   12.622%   $201.3456   $201.35   $201.35   $201.30  
  Purchase #7 $129.29   4.215%   $134.7396   $134.74   $134.75   $134.70  
  7 purchase totals = $1,103.57       $1,201.4862   $1,201.50   $1,201.55   $1,201.40