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 $54.32   12.479%   $61.0986   $61.10   $61.10   $61.10  
  Purchase #2 $172.77   11.782%   $193.1258   $193.13   $193.15   $193.10  
  Purchase #3 $226.82   9.515%   $248.4019   $248.40   $248.40   $248.40  
  Purchase #4 $231.54   6.394%   $246.3447   $246.34   $246.35   $246.30  
  Purchase #5 $175.61   12.555%   $197.6578   $197.66   $197.65   $197.70  
  Purchase #6 $5.60   6.430%   $5.9601   $5.96   $5.95   $6.00  
  Purchase #7 $197.94   11.871%   $221.4375   $221.44   $221.45   $221.40  
  7 purchase totals = $1,064.60       $1,174.0264   $1,174.03   $1,174.05   $1,174.00