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 $165.65   11.729%   $185.0791   $185.08   $185.10   $185.10  
  Purchase #2 $241.28   13.399%   $273.6091   $273.61   $273.60   $273.60  
  Purchase #3 $183.30   5.771%   $193.8782   $193.88   $193.90   $193.90  
  Purchase #4 $175.36   11.768%   $195.9964   $196.00   $196.00   $196.00  
  Purchase #5 $212.37   5.235%   $223.4876   $223.49   $223.50   $223.50  
  Purchase #6 $244.68   9.428%   $267.7484   $267.75   $267.75   $267.70  
  Purchase #7 $78.70   7.653%   $84.7229   $84.72   $84.70   $84.70  
  7 purchase totals = $1,301.34       $1,424.5217   $1,424.53   $1,424.55   $1,424.50