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 $64.99   12.871%   $73.3549   $73.35   $73.35   $73.40  
  Purchase #2 $163.74   9.462%   $179.2331   $179.23   $179.25   $179.20  
  Purchase #3 $166.52   12.157%   $186.7638   $186.76   $186.75   $186.80  
  Purchase #4 $216.40   6.626%   $230.7387   $230.74   $230.75   $230.70  
  Purchase #5 $53.30   11.152%   $59.244   $59.24   $59.25   $59.20  
  Purchase #6 $93.44   10.818%   $103.5483   $103.55   $103.55   $103.50  
  Purchase #7 $153.98   9.329%   $168.3448   $168.34   $168.35   $168.30  
  7 purchase totals = $912.37       $1,001.2276   $1,001.21   $1,001.25   $1,001.10