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 $27.76   10.716%   $30.7348   $30.73   $30.75   $30.70  
  Purchase #2 $154.55   6.780%   $165.0285   $165.03   $165.05   $165.00  
  Purchase #3 $193.32   5.299%   $203.564   $203.56   $203.55   $203.60  
  Purchase #4 $30.50   10.601%   $33.7333   $33.73   $33.75   $33.70  
  Purchase #5 $103.84   11.769%   $116.0609   $116.06   $116.05   $116.10  
  Purchase #6 $217.27   13.393%   $246.369   $246.37   $246.35   $246.40  
  Purchase #7 $204.71   10.440%   $226.0817   $226.08   $226.10   $226.10  
  7 purchase totals = $931.95       $1,021.5722   $1,021.56   $1,021.60   $1,021.60