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 $204.84   10.737%   $226.8337   $226.83   $226.85   $226.80  
  Purchase #2 $24.49   5.545%   $25.848   $25.85   $25.85   $25.80  
  Purchase #3 $120.88   11.380%   $134.6361   $134.64   $134.65   $134.60  
  Purchase #4 $151.96   11.426%   $169.3229   $169.32   $169.30   $169.30  
  Purchase #5 $175.96   12.515%   $197.9814   $197.98   $198.00   $198.00  
  Purchase #6 $108.42   5.323%   $114.1912   $114.19   $114.20   $114.20  
  Purchase #7 $213.42   11.694%   $238.3773   $238.38   $238.40   $238.40  
  7 purchase totals = $999.97       $1,107.1906   $1,107.19   $1,107.25   $1,107.10