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 $80.73   5.177%   $84.9094   $84.91   $84.90   $84.90  
  Purchase #2 $246.81   11.725%   $275.7485   $275.75   $275.75   $275.70  
  Purchase #3 $155.63   5.468%   $164.1398   $164.14   $164.15   $164.10  
  Purchase #4 $219.82   7.231%   $235.7152   $235.72   $235.70   $235.70  
  Purchase #5 $213.77   11.427%   $238.1975   $238.20   $238.20   $238.20  
  Purchase #6 $107.65   4.293%   $112.2714   $112.27   $112.25   $112.30  
  Purchase #7 $71.65   11.686%   $80.023   $80.02   $80.00   $80.00  
  7 purchase totals = $1,096.06       $1,191.0048   $1,191.01   $1,190.95   $1,190.90