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 $158.28   3.507%   $163.8309   $163.83   $163.85   $163.80  
  Purchase #2 $119.64   13.383%   $135.6514   $135.65   $135.65   $135.70  
  Purchase #3 $235.34   13.840%   $267.9111   $267.91   $267.90   $267.90  
  Purchase #4 $249.97   7.803%   $269.4752   $269.48   $269.50   $269.50  
  Purchase #5 $237.34   10.520%   $262.3082   $262.31   $262.30   $262.30  
  Purchase #6 $204.67   13.123%   $231.5288   $231.53   $231.55   $231.50  
  Purchase #7 $39.58   3.599%   $41.0045   $41.00   $41.00   $41.00  
  7 purchase totals = $1,244.82       $1,371.7101   $1,371.71   $1,371.75   $1,371.70