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 $26.73   9.516%   $29.2736   $29.27   $29.25   $29.30  
  Purchase #2 $231.37   8.241%   $250.4372   $250.44   $250.45   $250.40  
  Purchase #3 $155.78   13.145%   $176.2573   $176.26   $176.25   $176.30  
  Purchase #4 $52.45   11.253%   $58.3522   $58.35   $58.35   $58.40  
  Purchase #5 $167.33   7.255%   $179.4698   $179.47   $179.45   $179.50  
  Purchase #6 $246.53   3.254%   $254.5521   $254.55   $254.55   $254.60  
  Purchase #7 $132.33   12.589%   $148.989   $148.99   $149.00   $149.00  
  7 purchase totals = $1,012.52       $1,097.3312   $1,097.33   $1,097.30   $1,097.50