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 $163.52   6.165%   $173.601   $173.60   $173.60   $173.60  
  Purchase #2 $96.55   9.326%   $105.5543   $105.55   $105.55   $105.60  
  Purchase #3 $44.42   11.671%   $49.6043   $49.60   $49.60   $49.60  
  Purchase #4 $243.29   6.831%   $259.9091   $259.91   $259.90   $259.90  
  Purchase #5 $211.57   9.136%   $230.899   $230.90   $230.90   $230.90  
  Purchase #6 $34.25   5.683%   $36.1964   $36.20   $36.20   $36.20  
  Purchase #7 $204.94   12.313%   $230.1743   $230.17   $230.15   $230.20  
  7 purchase totals = $998.54       $1,085.9384   $1,085.93   $1,085.90   $1,086.00