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 $56.66   8.206%   $61.3095   $61.31   $61.30   $61.30  
  Purchase #2 $99.77   8.135%   $107.8863   $107.89   $107.90   $107.90  
  Purchase #3 $149.36   8.456%   $161.9899   $161.99   $162.00   $162.00  
  Purchase #4 $108.61   7.592%   $116.8557   $116.86   $116.85   $116.90  
  Purchase #5 $17.88   4.416%   $18.6696   $18.67   $18.65   $18.70  
  Purchase #6 $190.77   3.815%   $198.0479   $198.05   $198.05   $198.00  
  Purchase #7 $228.40   12.809%   $257.6558   $257.66   $257.65   $257.70  
  7 purchase totals = $851.45       $922.4147   $922.43   $922.40   $922.50