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 $192.87   6.569%   $205.5396   $205.54   $205.55   $205.50  
  Purchase #2 $204.38   11.825%   $228.5479   $228.55   $228.55   $228.50  
  Purchase #3 $135.98   5.593%   $143.5854   $143.59   $143.60   $143.60  
  Purchase #4 $98.98   8.704%   $107.5952   $107.60   $107.60   $107.60  
  Purchase #5 $94.82   8.363%   $102.7498   $102.75   $102.75   $102.70  
  Purchase #6 $100.74   4.371%   $105.1433   $105.14   $105.15   $105.10  
  Purchase #7 $48.95   11.621%   $54.6385   $54.64   $54.65   $54.60  
  7 purchase totals = $876.72       $947.7997   $947.81   $947.85   $947.60