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 $48.51   5.664%   $51.2576   $51.26   $51.25   $51.30  
  Purchase #2 $146.28   3.579%   $151.5154   $151.52   $151.50   $151.50  
  Purchase #3 $193.87   13.269%   $219.5946   $219.59   $219.60   $219.60  
  Purchase #4 $205.91   12.468%   $231.5829   $231.58   $231.60   $231.60  
  Purchase #5 $235.45   11.457%   $262.4255   $262.43   $262.45   $262.40  
  Purchase #6 $209.72   3.501%   $217.0623   $217.06   $217.05   $217.10  
  Purchase #7 $214.81   6.481%   $228.7318   $228.73   $228.75   $228.70  
  7 purchase totals = $1,254.55       $1,362.1701   $1,362.17   $1,362.20   $1,362.20