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 $244.33   11.157%   $271.5899   $271.59   $271.60   $271.60  
  Purchase #2 $165.45   12.562%   $186.2338   $186.23   $186.25   $186.20  
  Purchase #3 $68.48   5.674%   $72.3656   $72.37   $72.35   $72.40  
  Purchase #4 $54.32   5.493%   $57.3038   $57.30   $57.30   $57.30  
  Purchase #5 $216.27   3.642%   $224.1466   $224.15   $224.15   $224.10  
  Purchase #6 $180.88   13.187%   $204.7326   $204.73   $204.75   $204.70  
  Purchase #7 $247.36   12.655%   $278.6634   $278.66   $278.65   $278.70  
  7 purchase totals = $1,177.09       $1,295.0357   $1,295.03   $1,295.05   $1,295.00