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 $63.77   7.652%   $68.6497   $68.65   $68.65   $68.60  
  Purchase #2 $125.45   11.794%   $140.2456   $140.25   $140.25   $140.20  
  Purchase #3 $23.52   9.288%   $25.7045   $25.70   $25.70   $25.70  
  Purchase #4 $168.44   5.843%   $178.2819   $178.28   $178.30   $178.30  
  Purchase #5 $231.67   7.113%   $248.1487   $248.15   $248.15   $248.10  
  Purchase #6 $241.46   6.412%   $256.9424   $256.94   $256.95   $256.90  
  Purchase #7 $218.64   7.449%   $234.9265   $234.93   $234.95   $234.90  
  7 purchase totals = $1,072.95       $1,152.8993   $1,152.90   $1,152.95   $1,152.70