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 $108.93   8.259%   $117.9265   $117.93   $117.95   $117.90  
  Purchase #2 $221.55   8.620%   $240.6476   $240.65   $240.65   $240.60  
  Purchase #3 $202.92   4.762%   $212.5831   $212.58   $212.60   $212.60  
  Purchase #4 $161.69   4.503%   $168.9709   $168.97   $168.95   $169.00  
  Purchase #5 $238.29   8.689%   $258.995   $259.00   $259.00   $259.00  
  Purchase #6 $244.66   7.608%   $263.2737   $263.27   $263.25   $263.30  
  Purchase #7 $175.51   12.364%   $197.2101   $197.21   $197.20   $197.20  
  7 purchase totals = $1,353.55       $1,459.6069   $1,459.61   $1,459.60   $1,459.60