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 $114.51   3.537%   $118.5602   $118.56   $118.55   $118.60  
  Purchase #2 $158.85   7.665%   $171.0259   $171.03   $171.05   $171.00  
  Purchase #3 $173.72   8.233%   $188.0224   $188.02   $188.00   $188.00  
  Purchase #4 $249.40   6.111%   $264.6408   $264.64   $264.65   $264.60  
  Purchase #5 $11.57   10.281%   $12.7595   $12.76   $12.75   $12.80  
  Purchase #6 $248.75   8.330%   $269.4709   $269.47   $269.45   $269.50  
  Purchase #7 $84.52   12.557%   $95.1332   $95.13   $95.15   $95.10  
  7 purchase totals = $1,041.32       $1,119.6129   $1,119.61   $1,119.60   $1,119.60