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 $198.86   4.244%   $207.2996   $207.30   $207.30   $207.30  
  Purchase #2 $222.79   8.217%   $241.0967   $241.10   $241.10   $241.10  
  Purchase #3 $90.99   13.211%   $103.0107   $103.01   $103.00   $103.00  
  Purchase #4 $35.39   3.479%   $36.6212   $36.62   $36.60   $36.60  
  Purchase #5 $246.41   5.258%   $259.3662   $259.37   $259.35   $259.40  
  Purchase #6 $169.60   9.394%   $185.5322   $185.53   $185.55   $185.50  
  Purchase #7 $76.66   13.415%   $86.9439   $86.94   $86.95   $86.90  
  7 purchase totals = $1,040.70       $1,119.8705   $1,119.87   $1,119.85   $1,119.80