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 $60.44   9.683%   $66.2924   $66.29   $66.30   $66.30  
  Purchase #2 $86.97   10.767%   $96.3341   $96.33   $96.35   $96.30  
  Purchase #3 $80.70   8.220%   $87.3335   $87.33   $87.35   $87.30  
  Purchase #4 $131.92   7.145%   $141.3457   $141.35   $141.35   $141.30  
  Purchase #5 $243.26   7.580%   $261.6991   $261.70   $261.70   $261.70  
  Purchase #6 $83.33   8.356%   $90.2931   $90.29   $90.30   $90.30  
  Purchase #7 $48.58   12.554%   $54.6787   $54.68   $54.70   $54.70  
  7 purchase totals = $735.20       $797.9766   $797.97   $798.05   $797.90