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 $49.30   8.515%   $53.4979   $53.50   $53.50   $53.50  
  Purchase #2 $203.81   11.258%   $226.7549   $226.75   $226.75   $226.80  
  Purchase #3 $109.62   8.490%   $118.9267   $118.93   $118.95   $118.90  
  Purchase #4 $239.84   11.208%   $266.7213   $266.72   $266.70   $266.70  
  Purchase #5 $167.33   6.627%   $178.419   $178.42   $178.40   $178.40  
  Purchase #6 $247.33   7.792%   $266.602   $266.60   $266.60   $266.60  
  Purchase #7 $77.45   7.669%   $83.3896   $83.39   $83.40   $83.40  
  7 purchase totals = $1,094.68       $1,194.3114   $1,194.31   $1,194.30   $1,194.30