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 $235.67   9.250%   $257.4695   $257.47   $257.45   $257.50  
  Purchase #2 $215.50   13.157%   $243.8533   $243.85   $243.85   $243.90  
  Purchase #3 $61.40   3.822%   $63.7467   $63.75   $63.75   $63.70  
  Purchase #4 $114.62   8.485%   $124.3455   $124.35   $124.35   $124.30  
  Purchase #5 $245.46   8.262%   $265.7399   $265.74   $265.75   $265.70  
  Purchase #6 $68.71   12.751%   $77.4712   $77.47   $77.45   $77.50  
  Purchase #7 $34.70   5.145%   $36.4853   $36.49   $36.50   $36.50  
  7 purchase totals = $976.06       $1,069.1114   $1,069.12   $1,069.10   $1,069.10