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 $50.32   6.403%   $53.542   $53.54   $53.55   $53.50  
  Purchase #2 $113.74   4.221%   $118.541   $118.54   $118.55   $118.50  
  Purchase #3 $113.92   3.661%   $118.0906   $118.09   $118.10   $118.10  
  Purchase #4 $218.39   3.861%   $226.822   $226.82   $226.80   $226.80  
  Purchase #5 $98.44   11.821%   $110.0766   $110.08   $110.10   $110.10  
  Purchase #6 $113.71   5.393%   $119.8424   $119.84   $119.85   $119.80  
  Purchase #7 $103.97   6.694%   $110.9298   $110.93   $110.95   $110.90  
  7 purchase totals = $812.49       $857.8444   $857.84   $857.90   $857.70