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 $151.79   13.611%   $172.4501   $172.45   $172.45   $172.50  
  Purchase #2 $28.80   13.113%   $32.5765   $32.58   $32.60   $32.60  
  Purchase #3 $201.94   9.653%   $221.4333   $221.43   $221.45   $221.40  
  Purchase #4 $100.33   12.843%   $113.2154   $113.22   $113.20   $113.20  
  Purchase #5 $218.99   11.852%   $244.9447   $244.94   $244.95   $244.90  
  Purchase #6 $14.39   6.444%   $15.3173   $15.32   $15.30   $15.30  
  Purchase #7 $120.62   3.364%   $124.6777   $124.68   $124.70   $124.70  
  7 purchase totals = $836.86       $924.6150   $924.62   $924.65   $924.60