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 $57.62   10.521%   $63.6822   $63.68   $63.70   $63.70  
  Purchase #2 $150.29   3.767%   $155.9514   $155.95   $155.95   $156.00  
  Purchase #3 $90.67   9.458%   $99.2456   $99.25   $99.25   $99.20  
  Purchase #4 $197.76   13.805%   $225.0608   $225.06   $225.05   $225.10  
  Purchase #5 $38.81   12.284%   $43.5774   $43.58   $43.60   $43.60  
  Purchase #6 $218.25   12.798%   $246.1816   $246.18   $246.20   $246.20  
  Purchase #7 $227.96   4.241%   $237.6278   $237.63   $237.65   $237.60  
  7 purchase totals = $981.36       $1,071.3268   $1,071.33   $1,071.40   $1,071.40