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 $54.85   11.808%   $61.3267   $61.33   $61.35   $61.30  
  Purchase #2 $50.94   8.602%   $55.3219   $55.32   $55.30   $55.30  
  Purchase #3 $171.62   7.221%   $184.0127   $184.01   $184.00   $184.00  
  Purchase #4 $81.87   3.694%   $84.8943   $84.89   $84.90   $84.90  
  Purchase #5 $240.28   11.747%   $268.5057   $268.51   $268.50   $268.50  
  Purchase #6 $185.42   4.849%   $194.411   $194.41   $194.40   $194.40  
  Purchase #7 $165.37   8.513%   $179.4479   $179.45   $179.45   $179.40  
  7 purchase totals = $950.35       $1,027.9202   $1,027.92   $1,027.90   $1,027.80