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 $56.32   5.702%   $59.5314   $59.53   $59.55   $59.50  
  Purchase #2 $177.99   10.590%   $196.8391   $196.84   $196.85   $196.80  
  Purchase #3 $37.75   10.391%   $41.6726   $41.67   $41.65   $41.70  
  Purchase #4 $21.48   11.294%   $23.906   $23.91   $23.90   $23.90  
  Purchase #5 $204.64   8.489%   $222.0119   $222.01   $222.00   $222.00  
  Purchase #6 $32.95   3.256%   $34.0229   $34.02   $34.00   $34.00  
  Purchase #7 $132.50   3.324%   $136.9043   $136.90   $136.90   $136.90  
  7 purchase totals = $663.63       $714.8882   $714.88   $714.85   $714.80