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 $25.85   3.350%   $26.716   $26.72   $26.70   $26.70  
  Purchase #2 $232.29   6.242%   $246.7895   $246.79   $246.80   $246.80  
  Purchase #3 $248.65   12.847%   $280.5941   $280.59   $280.60   $280.60  
  Purchase #4 $70.87   3.708%   $73.4979   $73.50   $73.50   $73.50  
  Purchase #5 $94.57   12.453%   $106.3468   $106.35   $106.35   $106.30  
  Purchase #6 $72.96   4.606%   $76.3205   $76.32   $76.30   $76.30  
  Purchase #7 $218.34   12.579%   $245.805   $245.81   $245.80   $245.80  
  7 purchase totals = $963.53       $1,056.0698   $1,056.08   $1,056.05   $1,056.00