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 $59.50   6.194%   $63.1854   $63.19   $63.20   $63.20  
  Purchase #2 $208.41   3.699%   $216.1191   $216.12   $216.10   $216.10  
  Purchase #3 $208.35   5.412%   $219.6259   $219.63   $219.65   $219.60  
  Purchase #4 $218.77   5.224%   $230.1985   $230.20   $230.20   $230.20  
  Purchase #5 $87.44   7.813%   $94.2717   $94.27   $94.25   $94.30  
  Purchase #6 $95.84   6.417%   $101.9901   $101.99   $102.00   $102.00  
  Purchase #7 $226.66   12.288%   $254.512   $254.51   $254.50   $254.50  
  7 purchase totals = $1,104.97       $1,179.9027   $1,179.91   $1,179.90   $1,179.90