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 $98.61   7.667%   $106.1704   $106.17   $106.15   $106.20  
  Purchase #2 $107.77   9.351%   $117.8476   $117.85   $117.85   $117.80  
  Purchase #3 $239.25   12.664%   $269.5486   $269.55   $269.55   $269.50  
  Purchase #4 $94.96   7.747%   $102.3166   $102.32   $102.30   $102.30  
  Purchase #5 $133.58   13.805%   $152.0207   $152.02   $152.00   $152.00  
  Purchase #6 $182.97   12.856%   $206.4926   $206.49   $206.50   $206.50  
  Purchase #7 $58.42   11.345%   $65.0477   $65.05   $65.05   $65.00  
  7 purchase totals = $915.56       $1,019.4442   $1,019.45   $1,019.40   $1,019.30