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 $84.91   12.522%   $95.5424   $95.54   $95.55   $95.50  
  Purchase #2 $164.30   5.531%   $173.3874   $173.39   $173.40   $173.40  
  Purchase #3 $115.39   12.604%   $129.9338   $129.93   $129.95   $129.90  
  Purchase #4 $155.37   9.274%   $169.779   $169.78   $169.80   $169.80  
  Purchase #5 $68.60   8.552%   $74.4667   $74.47   $74.45   $74.50  
  Purchase #6 $235.32   6.516%   $250.6535   $250.65   $250.65   $250.70  
  Purchase #7 $128.37   8.546%   $139.3405   $139.34   $139.35   $139.30  
  7 purchase totals = $952.26       $1,033.1033   $1,033.10   $1,033.15   $1,033.10