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 $212.91   9.241%   $232.585   $232.59   $232.60   $232.60  
  Purchase #2 $158.63   6.289%   $168.6062   $168.61   $168.60   $168.60  
  Purchase #3 $76.90   8.372%   $83.3381   $83.34   $83.35   $83.30  
  Purchase #4 $213.92   5.283%   $225.2214   $225.22   $225.20   $225.20  
  Purchase #5 $167.85   12.437%   $188.7255   $188.73   $188.75   $188.70  
  Purchase #6 $73.52   3.453%   $76.0586   $76.06   $76.05   $76.10  
  Purchase #7 $48.69   6.103%   $51.6616   $51.66   $51.65   $51.70  
  7 purchase totals = $952.42       $1,026.1964   $1,026.21   $1,026.20   $1,026.20