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 $246.27   5.668%   $260.2286   $260.23   $260.25   $260.20  
  Purchase #2 $47.33   13.386%   $53.6656   $53.67   $53.65   $53.70  
  Purchase #3 $93.71   13.508%   $106.3683   $106.37   $106.35   $106.40  
  Purchase #4 $238.33   8.136%   $257.7205   $257.72   $257.70   $257.70  
  Purchase #5 $225.87   3.537%   $233.859   $233.86   $233.85   $233.90  
  Purchase #6 $6.59   11.351%   $7.338   $7.34   $7.35   $7.30  
  Purchase #7 $156.79   11.451%   $174.744   $174.74   $174.75   $174.70  
  7 purchase totals = $1,014.89       $1,093.9240   $1,093.93   $1,093.90   $1,093.90