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 $242.96   8.641%   $263.9542   $263.95   $263.95   $264.00  
  Purchase #2 $64.67   6.433%   $68.8302   $68.83   $68.85   $68.80  
  Purchase #3 $203.84   3.631%   $211.2414   $211.24   $211.25   $211.20  
  Purchase #4 $8.84   3.854%   $9.1807   $9.18   $9.20   $9.20  
  Purchase #5 $172.84   12.597%   $194.6127   $194.61   $194.60   $194.60  
  Purchase #6 $43.76   6.481%   $46.5961   $46.60   $46.60   $46.60  
  Purchase #7 $119.94   7.734%   $129.2162   $129.22   $129.20   $129.20  
  7 purchase totals = $856.85       $923.6315   $923.63   $923.65   $923.60