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 $61.26   10.374%   $67.6151   $67.62   $67.60   $67.60  
  Purchase #2 $54.44   13.214%   $61.6337   $61.63   $61.65   $61.60  
  Purchase #3 $39.53   3.683%   $40.9859   $40.99   $41.00   $41.00  
  Purchase #4 $151.98   3.822%   $157.7887   $157.79   $157.80   $157.80  
  Purchase #5 $166.90   4.728%   $174.791   $174.79   $174.80   $174.80  
  Purchase #6 $202.52   4.527%   $211.6881   $211.69   $211.70   $211.70  
  Purchase #7 $190.89   12.219%   $214.2148   $214.21   $214.20   $214.20  
  7 purchase totals = $867.52       $928.7173   $928.72   $928.75   $928.70