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 $197.58   5.278%   $208.0083   $208.01   $208.00   $208.00  
  Purchase #2 $23.65   4.415%   $24.6941   $24.69   $24.70   $24.70  
  Purchase #3 $28.74   6.571%   $30.6285   $30.63   $30.65   $30.60  
  Purchase #4 $87.58   6.606%   $93.3655   $93.37   $93.35   $93.40  
  Purchase #5 $93.70   13.439%   $106.2923   $106.29   $106.30   $106.30  
  Purchase #6 $171.45   9.449%   $187.6503   $187.65   $187.65   $187.70  
  Purchase #7 $187.50   10.502%   $207.1913   $207.19   $207.20   $207.20  
  7 purchase totals = $790.20       $857.8303   $857.83   $857.85   $857.90