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 $63.84   7.434%   $68.5859   $68.59   $68.60   $68.60  
  Purchase #2 $102.82   4.527%   $107.4747   $107.47   $107.45   $107.50  
  Purchase #3 $219.89   10.110%   $242.1209   $242.12   $242.10   $242.10  
  Purchase #4 $181.41   11.372%   $202.0399   $202.04   $202.05   $202.00  
  Purchase #5 $90.67   10.183%   $99.9029   $99.90   $99.90   $99.90  
  Purchase #6 $66.54   4.443%   $69.4964   $69.50   $69.50   $69.50  
  Purchase #7 $217.27   4.448%   $226.9342   $226.93   $226.95   $226.90  
  7 purchase totals = $942.44       $1,016.5549   $1,016.55   $1,016.55   $1,016.50