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 $233.96   8.787%   $254.5181   $254.52   $254.50   $254.50  
  Purchase #2 $15.75   10.314%   $17.3745   $17.37   $17.35   $17.40  
  Purchase #3 $238.85   4.581%   $249.7917   $249.79   $249.80   $249.80  
  Purchase #4 $163.37   4.827%   $171.2559   $171.26   $171.25   $171.30  
  Purchase #5 $203.65   11.698%   $227.473   $227.47   $227.45   $227.50  
  Purchase #6 $73.58   7.342%   $78.9822   $78.98   $79.00   $79.00  
  Purchase #7 $15.69   13.463%   $17.8023   $17.80   $17.80   $17.80  
  7 purchase totals = $944.85       $1,017.1977   $1,017.19   $1,017.15   $1,017.30