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 $70.79   3.832%   $73.5027   $73.50   $73.50   $73.50  
  Purchase #2 $226.98   8.171%   $245.5265   $245.53   $245.55   $245.50  
  Purchase #3 $142.26   8.645%   $154.5584   $154.56   $154.55   $154.60  
  Purchase #4 $165.35   6.606%   $176.273   $176.27   $176.25   $176.30  
  Purchase #5 $190.98   4.822%   $200.1891   $200.19   $200.20   $200.20  
  Purchase #6 $181.37   12.146%   $203.3992   $203.40   $203.40   $203.40  
  Purchase #7 $8.34   9.503%   $9.1326   $9.13   $9.15   $9.10  
  7 purchase totals = $986.07       $1,062.5815   $1,062.58   $1,062.60   $1,062.60