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 $102.72   8.828%   $111.7881   $111.79   $111.80   $111.80  
  Purchase #2 $207.72   3.707%   $215.4202   $215.42   $215.40   $215.40  
  Purchase #3 $208.83   5.280%   $219.8562   $219.86   $219.85   $219.90  
  Purchase #4 $136.52   8.217%   $147.7378   $147.74   $147.75   $147.70  
  Purchase #5 $158.47   3.438%   $163.9182   $163.92   $163.90   $163.90  
  Purchase #6 $129.50   8.450%   $140.4428   $140.44   $140.45   $140.40  
  Purchase #7 $171.77   10.238%   $189.3558   $189.36   $189.35   $189.40  
  7 purchase totals = $1,115.53       $1,188.5191   $1,188.53   $1,188.50   $1,188.50