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 $231.72   8.761%   $252.021   $252.02   $252.00   $252.00  
  Purchase #2 $235.40   10.159%   $259.3143   $259.31   $259.30   $259.30  
  Purchase #3 $185.25   8.491%   $200.9796   $200.98   $201.00   $201.00  
  Purchase #4 $179.93   7.816%   $193.9933   $193.99   $194.00   $194.00  
  Purchase #5 $152.73   6.766%   $163.0637   $163.06   $163.05   $163.10  
  Purchase #6 $9.32   4.391%   $9.7292   $9.73   $9.75   $9.70  
  Purchase #7 $223.97   10.487%   $247.4577   $247.46   $247.45   $247.50  
  7 purchase totals = $1,218.32       $1,326.5588   $1,326.55   $1,326.55   $1,326.60