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 $85.30   12.582%   $96.0324   $96.03   $96.05   $96.00  
  Purchase #2 $221.58   11.467%   $246.9886   $246.99   $247.00   $247.00  
  Purchase #3 $236.58   13.605%   $268.7667   $268.77   $268.75   $268.80  
  Purchase #4 $83.44   10.664%   $92.338   $92.34   $92.35   $92.30  
  Purchase #5 $128.46   9.209%   $140.2899   $140.29   $140.30   $140.30  
  Purchase #6 $102.86   10.842%   $114.0121   $114.01   $114.00   $114.00  
  Purchase #7 $226.41   11.124%   $251.5958   $251.60   $251.60   $251.60  
  7 purchase totals = $1,084.63       $1,210.0235   $1,210.03   $1,210.05   $1,210.00