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 $235.58   11.467%   $262.594   $262.59   $262.60   $262.60  
  Purchase #2 $26.89   7.819%   $28.9925   $28.99   $29.00   $29.00  
  Purchase #3 $25.63   4.236%   $26.7157   $26.72   $26.70   $26.70  
  Purchase #4 $107.52   5.775%   $113.7293   $113.73   $113.75   $113.70  
  Purchase #5 $170.35   12.656%   $191.9095   $191.91   $191.90   $191.90  
  Purchase #6 $184.54   5.477%   $194.6473   $194.65   $194.65   $194.60  
  Purchase #7 $106.45   7.747%   $114.6967   $114.70   $114.70   $114.70  
  7 purchase totals = $856.96       $933.2850   $933.29   $933.30   $933.20