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 $136.53   13.424%   $154.8578   $154.86   $154.85   $154.90  
  Purchase #2 $204.48   9.304%   $223.5048   $223.50   $223.50   $223.50  
  Purchase #3 $245.63   11.820%   $274.6635   $274.66   $274.65   $274.70  
  Purchase #4 $24.80   12.383%   $27.871   $27.87   $27.85   $27.90  
  Purchase #5 $150.63   13.819%   $171.4456   $171.45   $171.45   $171.40  
  Purchase #6 $163.98   11.136%   $182.2408   $182.24   $182.25   $182.20  
  Purchase #7 $156.91   10.740%   $173.7621   $173.76   $173.75   $173.80  
  7 purchase totals = $1,082.96       $1,208.3456   $1,208.34   $1,208.30   $1,208.40