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 $246.80   8.263%   $267.1931   $267.19   $267.20   $267.20  
  Purchase #2 $177.96   11.552%   $198.5179   $198.52   $198.50   $198.50  
  Purchase #3 $67.47   13.793%   $76.7761   $76.78   $76.80   $76.80  
  Purchase #4 $250.49   9.266%   $273.7004   $273.70   $273.70   $273.70  
  Purchase #5 $227.41   9.426%   $248.8457   $248.85   $248.85   $248.80  
  Purchase #6 $67.54   8.200%   $73.0783   $73.08   $73.10   $73.10  
  Purchase #7 $21.99   6.346%   $23.3855   $23.39   $23.40   $23.40  
  7 purchase totals = $1,059.66       $1,161.4970   $1,161.51   $1,161.55   $1,161.50