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 $31.43   12.245%   $35.2786   $35.28   $35.30   $35.30  
  Purchase #2 $192.71   11.599%   $215.0624   $215.06   $215.05   $215.10  
  Purchase #3 $241.87   9.771%   $265.5031   $265.50   $265.50   $265.50  
  Purchase #4 $204.90   6.458%   $218.1324   $218.13   $218.15   $218.10  
  Purchase #5 $123.96   5.167%   $130.365   $130.37   $130.35   $130.40  
  Purchase #6 $130.53   5.608%   $137.8501   $137.85   $137.85   $137.90  
  Purchase #7 $246.29   11.654%   $274.9926   $274.99   $275.00   $275.00  
  7 purchase totals = $1,171.69       $1,277.1842   $1,277.18   $1,277.20   $1,277.30