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 $241.63   9.490%   $264.5607   $264.56   $264.55   $264.60  
  Purchase #2 $23.63   13.812%   $26.8938   $26.89   $26.90   $26.90  
  Purchase #3 $152.55   8.359%   $165.3017   $165.30   $165.30   $165.30  
  Purchase #4 $111.65   3.373%   $115.416   $115.42   $115.40   $115.40  
  Purchase #5 $139.90   6.526%   $149.0299   $149.03   $149.05   $149.00  
  Purchase #6 $176.93   7.485%   $190.1732   $190.17   $190.15   $190.20  
  Purchase #7 $226.28   9.192%   $247.0797   $247.08   $247.10   $247.10  
  7 purchase totals = $1,072.57       $1,158.4550   $1,158.45   $1,158.45   $1,158.50