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 $222.87   10.491%   $246.2513   $246.25   $246.25   $246.30  
  Purchase #2 $53.36   5.677%   $56.3892   $56.39   $56.40   $56.40  
  Purchase #3 $144.68   10.444%   $159.7904   $159.79   $159.80   $159.80  
  Purchase #4 $59.72   11.366%   $66.5078   $66.51   $66.50   $66.50  
  Purchase #5 $133.80   12.570%   $150.6187   $150.62   $150.60   $150.60  
  Purchase #6 $165.48   7.335%   $177.618   $177.62   $177.60   $177.60  
  Purchase #7 $166.97   3.286%   $172.4566   $172.46   $172.45   $172.50  
  7 purchase totals = $946.88       $1,029.6320   $1,029.64   $1,029.60   $1,029.70