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 $148.52   10.243%   $163.7329   $163.73   $163.75   $163.70  
  Purchase #2 $211.57   6.784%   $225.9229   $225.92   $225.90   $225.90  
  Purchase #3 $216.73   9.724%   $237.8048   $237.80   $237.80   $237.80  
  Purchase #4 $129.78   11.567%   $144.7917   $144.79   $144.80   $144.80  
  Purchase #5 $32.37   6.787%   $34.567   $34.57   $34.55   $34.60  
  Purchase #6 $162.69   5.683%   $171.9357   $171.94   $171.95   $171.90  
  Purchase #7 $38.27   3.277%   $39.5241   $39.52   $39.50   $39.50  
  7 purchase totals = $939.93       $1,018.2791   $1,018.27   $1,018.25   $1,018.20