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 $247.95   8.758%   $269.6655   $269.67   $269.65   $269.70  
  Purchase #2 $107.39   8.139%   $116.1305   $116.13   $116.15   $116.10  
  Purchase #3 $146.74   11.474%   $163.5769   $163.58   $163.60   $163.60  
  Purchase #4 $120.37   7.118%   $128.9379   $128.94   $128.95   $128.90  
  Purchase #5 $109.81   5.492%   $115.8408   $115.84   $115.85   $115.80  
  Purchase #6 $68.65   5.140%   $72.1786   $72.18   $72.20   $72.20  
  Purchase #7 $82.86   5.257%   $87.216   $87.22   $87.20   $87.20  
  7 purchase totals = $883.77       $953.5462   $953.56   $953.60   $953.50