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 $62.59   8.783%   $68.0873   $68.09   $68.10   $68.10  
  Purchase #2 $247.40   11.677%   $276.2889   $276.29   $276.30   $276.30  
  Purchase #3 $65.58   6.214%   $69.6551   $69.66   $69.65   $69.70  
  Purchase #4 $88.29   10.517%   $97.5755   $97.58   $97.60   $97.60  
  Purchase #5 $170.69   6.106%   $181.1123   $181.11   $181.10   $181.10  
  Purchase #6 $206.54   12.329%   $232.0043   $232.00   $232.00   $232.00  
  Purchase #7 $113.86   12.650%   $128.2633   $128.26   $128.25   $128.30  
  7 purchase totals = $954.95       $1,052.9867   $1,052.99   $1,053.00   $1,053.10