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 $241.75   11.352%   $269.1935   $269.19   $269.20   $269.20  
  Purchase #2 $48.55   9.374%   $53.1011   $53.10   $53.10   $53.10  
  Purchase #3 $145.43   11.481%   $162.1268   $162.13   $162.15   $162.10  
  Purchase #4 $5.39   8.772%   $5.8628   $5.86   $5.85   $5.90  
  Purchase #5 $179.63   5.552%   $189.6031   $189.60   $189.60   $189.60  
  Purchase #6 $8.48   6.314%   $9.0154   $9.02   $9.00   $9.00  
  Purchase #7 $106.65   6.152%   $113.2111   $113.21   $113.20   $113.20  
  7 purchase totals = $735.88       $802.1138   $802.11   $802.10   $802.10