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 $213.49   9.542%   $233.8612   $233.86   $233.85   $233.90  
  Purchase #2 $222.35   13.864%   $253.1766   $253.18   $253.20   $253.20  
  Purchase #3 $136.37   9.791%   $149.722   $149.72   $149.70   $149.70  
  Purchase #4 $245.30   4.374%   $256.0294   $256.03   $256.05   $256.00  
  Purchase #5 $23.58   5.232%   $24.8137   $24.81   $24.80   $24.80  
  Purchase #6 $71.81   4.303%   $74.9   $74.90   $74.90   $74.90  
  Purchase #7 $9.55   5.221%   $10.0486   $10.05   $10.05   $10.00  
  7 purchase totals = $922.45       $1,002.5515   $1,002.55   $1,002.55   $1,002.50