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 $175.73   12.454%   $197.6154   $197.62   $197.60   $197.60  
  Purchase #2 $20.47   3.827%   $21.2534   $21.25   $21.25   $21.30  
  Purchase #3 $226.26   11.719%   $252.7754   $252.78   $252.80   $252.80  
  Purchase #4 $14.83   13.479%   $16.8289   $16.83   $16.85   $16.80  
  Purchase #5 $225.98   9.348%   $247.1046   $247.10   $247.10   $247.10  
  Purchase #6 $221.69   10.236%   $244.3822   $244.38   $244.40   $244.40  
  Purchase #7 $40.52   7.320%   $43.4861   $43.49   $43.50   $43.50  
  7 purchase totals = $925.48       $1,023.4460   $1,023.45   $1,023.50   $1,023.50