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 $228.51   8.202%   $247.2524   $247.25   $247.25   $247.30  
  Purchase #2 $207.48   8.702%   $225.5349   $225.53   $225.55   $225.50  
  Purchase #3 $61.27   10.335%   $67.6023   $67.60   $67.60   $67.60  
  Purchase #4 $100.38   5.501%   $105.9019   $105.90   $105.90   $105.90  
  Purchase #5 $237.74   7.209%   $254.8787   $254.88   $254.90   $254.90  
  Purchase #6 $238.74   11.391%   $265.9349   $265.93   $265.95   $265.90  
  Purchase #7 $83.58   5.280%   $87.993   $87.99   $88.00   $88.00  
  7 purchase totals = $1,157.70       $1,255.0981   $1,255.08   $1,255.15   $1,255.10