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 $245.52   8.724%   $266.9392   $266.94   $266.95   $266.90  
  Purchase #2 $31.61   9.437%   $34.593   $34.59   $34.60   $34.60  
  Purchase #3 $130.55   5.310%   $137.4822   $137.48   $137.50   $137.50  
  Purchase #4 $113.63   11.201%   $126.3577   $126.36   $126.35   $126.40  
  Purchase #5 $137.59   10.321%   $151.7907   $151.79   $151.80   $151.80  
  Purchase #6 $123.86   10.180%   $136.4689   $136.47   $136.45   $136.50  
  Purchase #7 $203.42   9.532%   $222.81   $222.81   $222.80   $222.80  
  7 purchase totals = $986.18       $1,076.4417   $1,076.44   $1,076.45   $1,076.50