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 $221.58   5.598%   $233.984   $233.98   $234.00   $234.00  
  Purchase #2 $197.94   10.428%   $218.5812   $218.58   $218.60   $218.60  
  Purchase #3 $20.40   10.494%   $22.5408   $22.54   $22.55   $22.50  
  Purchase #4 $66.43   6.518%   $70.7599   $70.76   $70.75   $70.80  
  Purchase #5 $183.69   8.223%   $198.7948   $198.79   $198.80   $198.80  
  Purchase #6 $30.68   5.270%   $32.2968   $32.30   $32.30   $32.30  
  Purchase #7 $207.55   11.423%   $231.2584   $231.26   $231.25   $231.30  
  7 purchase totals = $928.27       $1,008.2159   $1,008.21   $1,008.25   $1,008.30