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 $202.69   7.717%   $218.3316   $218.33   $218.35   $218.30  
  Purchase #2 $106.60   6.159%   $113.1655   $113.17   $113.15   $113.20  
  Purchase #3 $84.29   6.751%   $89.9804   $89.98   $90.00   $90.00  
  Purchase #4 $92.58   6.172%   $98.294   $98.29   $98.30   $98.30  
  Purchase #5 $188.55   3.176%   $194.5383   $194.54   $194.55   $194.50  
  Purchase #6 $56.68   5.337%   $59.705   $59.71   $59.70   $59.70  
  Purchase #7 $236.26   7.272%   $253.4408   $253.44   $253.45   $253.40  
  7 purchase totals = $967.65       $1,027.4556   $1,027.46   $1,027.50   $1,027.40