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 $211.27   13.135%   $239.0203   $239.02   $239.00   $239.00  
  Purchase #2 $31.71   12.574%   $35.6972   $35.70   $35.70   $35.70  
  Purchase #3 $181.78   12.236%   $204.0226   $204.02   $204.00   $204.00  
  Purchase #4 $35.56   9.432%   $38.914   $38.91   $38.90   $38.90  
  Purchase #5 $246.64   13.483%   $279.8945   $279.89   $279.90   $279.90  
  Purchase #6 $101.69   3.435%   $105.1831   $105.18   $105.20   $105.20  
  Purchase #7 $199.41   12.265%   $223.8676   $223.87   $223.85   $223.90  
  7 purchase totals = $1,008.06       $1,126.5993   $1,126.59   $1,126.55   $1,126.60