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 $191.50   8.233%   $207.2662   $207.27   $207.25   $207.30  
  Purchase #2 $145.52   9.838%   $159.8363   $159.84   $159.85   $159.80  
  Purchase #3 $156.66   5.747%   $165.6633   $165.66   $165.65   $165.70  
  Purchase #4 $77.25   8.593%   $83.8881   $83.89   $83.90   $83.90  
  Purchase #5 $184.85   11.443%   $206.0024   $206.00   $206.00   $206.00  
  Purchase #6 $213.80   6.601%   $227.9129   $227.91   $227.90   $227.90  
  Purchase #7 $116.81   6.338%   $124.2134   $124.21   $124.20   $124.20  
  7 purchase totals = $1,086.39       $1,174.7826   $1,174.78   $1,174.75   $1,174.80