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 $50.98   11.679%   $56.934   $56.93   $56.95   $56.90  
  Purchase #2 $244.62   3.538%   $253.2747   $253.27   $253.25   $253.30  
  Purchase #3 $229.26   5.643%   $242.1971   $242.20   $242.20   $242.20  
  Purchase #4 $67.71   7.743%   $72.9528   $72.95   $72.95   $73.00  
  Purchase #5 $219.52   5.615%   $231.846   $231.85   $231.85   $231.80  
  Purchase #6 $24.93   12.410%   $28.0238   $28.02   $28.00   $28.00  
  Purchase #7 $15.61   13.507%   $17.7184   $17.72   $17.70   $17.70  
  7 purchase totals = $852.63       $902.9468   $902.94   $902.90   $902.90