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 $201.64   5.268%   $212.2624   $212.26   $212.25   $212.30  
  Purchase #2 $109.69   3.656%   $113.7003   $113.70   $113.70   $113.70  
  Purchase #3 $34.26   5.780%   $36.2402   $36.24   $36.25   $36.20  
  Purchase #4 $153.30   4.649%   $160.4269   $160.43   $160.45   $160.40  
  Purchase #5 $226.72   10.410%   $250.3216   $250.32   $250.30   $250.30  
  Purchase #6 $118.92   13.111%   $134.5116   $134.51   $134.50   $134.50  
  Purchase #7 $122.87   10.436%   $135.6927   $135.69   $135.70   $135.70  
  7 purchase totals = $967.40       $1,043.1557   $1,043.15   $1,043.15   $1,043.10