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 $23.91   11.670%   $26.7003   $26.70   $26.70   $26.70  
  Purchase #2 $222.42   9.307%   $243.1206   $243.12   $243.10   $243.10  
  Purchase #3 $87.95   6.128%   $93.3396   $93.34   $93.35   $93.30  
  Purchase #4 $54.93   13.636%   $62.4203   $62.42   $62.40   $62.40  
  Purchase #5 $189.77   3.143%   $195.7345   $195.73   $195.75   $195.70  
  Purchase #6 $214.91   5.558%   $226.8547   $226.85   $226.85   $226.90  
  Purchase #7 $137.51   13.424%   $155.9693   $155.97   $155.95   $156.00  
  7 purchase totals = $931.40       $1,004.1393   $1,004.13   $1,004.10   $1,004.10