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 $223.66   11.150%   $248.5981   $248.60   $248.60   $248.60  
  Purchase #2 $184.34   9.195%   $201.2901   $201.29   $201.30   $201.30  
  Purchase #3 $241.94   11.295%   $269.2671   $269.27   $269.25   $269.30  
  Purchase #4 $118.79   8.607%   $129.0143   $129.01   $129.00   $129.00  
  Purchase #5 $10.55   3.560%   $10.9256   $10.93   $10.95   $10.90  
  Purchase #6 $167.87   8.415%   $181.9963   $182.00   $182.00   $182.00  
  Purchase #7 $118.26   13.695%   $134.4557   $134.46   $134.45   $134.50  
  7 purchase totals = $1,065.41       $1,175.5472   $1,175.56   $1,175.55   $1,175.60