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 $58.84   10.215%   $64.8505   $64.85   $64.85   $64.90  
  Purchase #2 $229.51   4.464%   $239.7553   $239.76   $239.75   $239.80  
  Purchase #3 $196.35   11.459%   $218.8497   $218.85   $218.85   $218.80  
  Purchase #4 $162.78   6.345%   $173.1084   $173.11   $173.10   $173.10  
  Purchase #5 $45.64   8.401%   $49.4742   $49.47   $49.45   $49.50  
  Purchase #6 $226.93   9.103%   $247.5874   $247.59   $247.60   $247.60  
  Purchase #7 $161.40   3.874%   $167.6526   $167.65   $167.65   $167.70  
  7 purchase totals = $1,081.45       $1,161.2781   $1,161.28   $1,161.25   $1,161.40