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 $145.52   12.773%   $164.1073   $164.11   $164.10   $164.10  
  Purchase #2 $228.63   11.479%   $254.8744   $254.87   $254.85   $254.90  
  Purchase #3 $224.69   10.649%   $248.6172   $248.62   $248.60   $248.60  
  Purchase #4 $156.82   11.417%   $174.7241   $174.72   $174.70   $174.70  
  Purchase #5 $189.32   6.406%   $201.4478   $201.45   $201.45   $201.40  
  Purchase #6 $70.68   3.196%   $72.9389   $72.94   $72.95   $72.90  
  Purchase #7 $78.58   7.346%   $84.3525   $84.35   $84.35   $84.40  
  7 purchase totals = $1,094.24       $1,201.0622   $1,201.06   $1,201.00   $1,201.00