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 $248.55   11.694%   $277.6154   $277.62   $277.60   $277.60  
  Purchase #2 $189.67   6.296%   $201.6116   $201.61   $201.60   $201.60  
  Purchase #3 $29.42   10.722%   $32.5744   $32.57   $32.55   $32.60  
  Purchase #4 $96.43   4.240%   $100.5186   $100.52   $100.50   $100.50  
  Purchase #5 $226.89   6.323%   $241.2363   $241.24   $241.25   $241.20  
  Purchase #6 $209.85   5.697%   $221.8052   $221.81   $221.80   $221.80  
  Purchase #7 $113.41   4.457%   $118.4647   $118.46   $118.45   $118.50  
  7 purchase totals = $1,114.22       $1,193.8262   $1,193.83   $1,193.75   $1,193.80