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 $187.87   8.456%   $203.7563   $203.76   $203.75   $203.80  
  Purchase #2 $206.94   5.616%   $218.5618   $218.56   $218.55   $218.60  
  Purchase #3 $237.76   4.394%   $248.2072   $248.21   $248.20   $248.20  
  Purchase #4 $248.67   5.280%   $261.7998   $261.80   $261.80   $261.80  
  Purchase #5 $68.59   5.807%   $72.573   $72.57   $72.55   $72.60  
  Purchase #6 $21.77   5.367%   $22.9384   $22.94   $22.95   $22.90  
  Purchase #7 $136.72   6.586%   $145.7244   $145.72   $145.70   $145.70  
  7 purchase totals = $1,108.32       $1,173.5609   $1,173.56   $1,173.50   $1,173.60