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 $54.55   11.116%   $60.6138   $60.61   $60.60   $60.60  
  Purchase #2 $205.79   5.170%   $216.4293   $216.43   $216.45   $216.40  
  Purchase #3 $50.76   8.290%   $54.968   $54.97   $54.95   $55.00  
  Purchase #4 $71.31   4.826%   $74.7514   $74.75   $74.75   $74.80  
  Purchase #5 $173.67   3.260%   $179.3316   $179.33   $179.35   $179.30  
  Purchase #6 $110.58   6.702%   $117.9911   $117.99   $118.00   $118.00  
  Purchase #7 $236.68   9.445%   $259.0344   $259.03   $259.05   $259.00  
  7 purchase totals = $903.34       $963.1196   $963.11   $963.15   $963.10