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 $54.41   13.871%   $61.9572   $61.96   $61.95   $62.00  
  Purchase #2 $220.95   10.807%   $244.8281   $244.83   $244.85   $244.80  
  Purchase #3 $75.69   12.641%   $85.258   $85.26   $85.25   $85.30  
  Purchase #4 $87.25   13.642%   $99.1526   $99.15   $99.15   $99.20  
  Purchase #5 $86.81   5.735%   $91.7886   $91.79   $91.80   $91.80  
  Purchase #6 $144.64   12.744%   $163.0729   $163.07   $163.05   $163.10  
  Purchase #7 $147.81   13.474%   $167.7259   $167.73   $167.75   $167.70  
  7 purchase totals = $817.56       $913.7833   $913.79   $913.80   $913.90