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 $176.53   7.311%   $189.4361   $189.44   $189.45   $189.40  
  Purchase #2 $163.32   7.106%   $174.9255   $174.93   $174.95   $174.90  
  Purchase #3 $213.97   11.224%   $237.986   $237.99   $238.00   $238.00  
  Purchase #4 $44.42   11.704%   $49.6189   $49.62   $49.60   $49.60  
  Purchase #5 $48.47   12.273%   $54.4187   $54.42   $54.40   $54.40  
  Purchase #6 $19.82   11.199%   $22.0396   $22.04   $22.05   $22.00  
  Purchase #7 $240.66   5.502%   $253.9011   $253.90   $253.90   $253.90  
  7 purchase totals = $907.19       $982.3259   $982.34   $982.35   $982.20