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 $23.47   4.741%   $24.5827   $24.58   $24.60   $24.60  
  Purchase #2 $112.88   7.487%   $121.3313   $121.33   $121.35   $121.30  
  Purchase #3 $204.35   9.110%   $222.9663   $222.97   $222.95   $223.00  
  Purchase #4 $209.81   6.233%   $222.8875   $222.89   $222.90   $222.90  
  Purchase #5 $141.34   8.651%   $153.5673   $153.57   $153.55   $153.60  
  Purchase #6 $243.38   9.315%   $266.0508   $266.05   $266.05   $266.10  
  Purchase #7 $49.46   3.547%   $51.2143   $51.21   $51.20   $51.20  
  7 purchase totals = $984.69       $1,062.6002   $1,062.60   $1,062.60   $1,062.70