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 $245.26   3.835%   $254.6657   $254.67   $254.65   $254.70  
  Purchase #2 $175.67   11.176%   $195.3029   $195.30   $195.30   $195.30  
  Purchase #3 $61.71   12.692%   $69.5422   $69.54   $69.55   $69.50  
  Purchase #4 $59.64   13.312%   $67.5793   $67.58   $67.60   $67.60  
  Purchase #5 $162.80   11.155%   $180.9603   $180.96   $180.95   $181.00  
  Purchase #6 $146.56   11.744%   $163.772   $163.77   $163.75   $163.80  
  Purchase #7 $86.78   12.325%   $97.4756   $97.48   $97.50   $97.50  
  7 purchase totals = $938.42       $1,029.2980   $1,029.30   $1,029.30   $1,029.40