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 $65.78   5.789%   $69.588   $69.59   $69.60   $69.60  
  Purchase #2 $108.84   9.217%   $118.8718   $118.87   $118.85   $118.90  
  Purchase #3 $216.91   9.184%   $236.831   $236.83   $236.85   $236.80  
  Purchase #4 $111.75   13.385%   $126.7077   $126.71   $126.70   $126.70  
  Purchase #5 $227.46   3.279%   $234.9184   $234.92   $234.90   $234.90  
  Purchase #6 $149.52   3.489%   $154.7368   $154.74   $154.75   $154.70  
  Purchase #7 $65.44   6.223%   $69.5123   $69.51   $69.50   $69.50  
  7 purchase totals = $945.70       $1,011.1660   $1,011.17   $1,011.15   $1,011.10