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 $239.84   10.747%   $265.6156   $265.62   $265.60   $265.60  
  Purchase #2 $165.94   6.772%   $177.1775   $177.18   $177.20   $177.20  
  Purchase #3 $167.83   13.858%   $191.0879   $191.09   $191.10   $191.10  
  Purchase #4 $59.87   10.548%   $66.1851   $66.19   $66.20   $66.20  
  Purchase #5 $197.95   3.270%   $204.423   $204.42   $204.40   $204.40  
  Purchase #6 $59.43   8.369%   $64.4037   $64.40   $64.40   $64.40  
  Purchase #7 $39.71   4.109%   $41.3417   $41.34   $41.35   $41.30  
  7 purchase totals = $930.57       $1,010.2345   $1,010.24   $1,010.25   $1,010.20