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 $218.73   11.772%   $244.4789   $244.48   $244.50   $244.50  
  Purchase #2 $51.75   7.394%   $55.5764   $55.58   $55.60   $55.60  
  Purchase #3 $207.27   6.525%   $220.7944   $220.79   $220.80   $220.80  
  Purchase #4 $29.39   7.261%   $31.524   $31.52   $31.50   $31.50  
  Purchase #5 $249.88   8.663%   $271.5271   $271.53   $271.55   $271.50  
  Purchase #6 $163.76   4.394%   $170.9556   $170.96   $170.95   $171.00  
  Purchase #7 $25.90   7.361%   $27.8065   $27.81   $27.80   $27.80  
  7 purchase totals = $946.68       $1,022.6629   $1,022.67   $1,022.70   $1,022.70