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 $85.81   12.200%   $96.2788   $96.28   $96.30   $96.30  
  Purchase #2 $240.75   13.418%   $273.0538   $273.05   $273.05   $273.10  
  Purchase #3 $23.47   4.182%   $24.4515   $24.45   $24.45   $24.50  
  Purchase #4 $49.95   4.743%   $52.3191   $52.32   $52.30   $52.30  
  Purchase #5 $194.78   4.424%   $203.3971   $203.40   $203.40   $203.40  
  Purchase #6 $90.75   12.817%   $102.3814   $102.38   $102.40   $102.40  
  Purchase #7 $242.55   7.587%   $260.9523   $260.95   $260.95   $261.00  
  7 purchase totals = $928.06       $1,012.8340   $1,012.83   $1,012.85   $1,013.00