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 $53.94   3.149%   $55.6386   $55.64   $55.65   $55.60  
  Purchase #2 $196.95   13.336%   $223.2153   $223.22   $223.20   $223.20  
  Purchase #3 $24.35   3.419%   $25.1825   $25.18   $25.20   $25.20  
  Purchase #4 $73.61   13.661%   $83.6659   $83.67   $83.65   $83.70  
  Purchase #5 $244.71   6.169%   $259.8062   $259.81   $259.80   $259.80  
  Purchase #6 $41.56   7.247%   $44.5719   $44.57   $44.55   $44.60  
  Purchase #7 $11.37   11.175%   $12.6406   $12.64   $12.65   $12.60  
  7 purchase totals = $646.49       $704.7210   $704.73   $704.70   $704.70