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 $212.94   3.628%   $220.6655   $220.67   $220.65   $220.70  
  Purchase #2 $147.78   4.684%   $154.702   $154.70   $154.70   $154.70  
  Purchase #3 $55.67   4.106%   $57.9558   $57.96   $57.95   $58.00  
  Purchase #4 $177.73   4.139%   $185.0862   $185.09   $185.10   $185.10  
  Purchase #5 $144.93   11.619%   $161.7694   $161.77   $161.75   $161.80  
  Purchase #6 $178.32   4.666%   $186.6404   $186.64   $186.65   $186.60  
  Purchase #7 $246.94   12.483%   $277.7655   $277.77   $277.75   $277.80  
  7 purchase totals = $1,164.31       $1,244.5848   $1,244.60   $1,244.55   $1,244.70