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 $56.81   7.477%   $61.0577   $61.06   $61.05   $61.10  
  Purchase #2 $141.74   4.301%   $147.8362   $147.84   $147.85   $147.80  
  Purchase #3 $184.31   6.195%   $195.728   $195.73   $195.75   $195.70  
  Purchase #4 $101.25   7.114%   $108.4529   $108.45   $108.45   $108.50  
  Purchase #5 $210.41   8.773%   $228.8693   $228.87   $228.85   $228.90  
  Purchase #6 $201.39   8.336%   $218.1779   $218.18   $218.20   $218.20  
  Purchase #7 $28.93   11.682%   $32.3096   $32.31   $32.30   $32.30  
  7 purchase totals = $924.84       $992.4316   $992.44   $992.45   $992.50