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 $71.39   6.521%   $76.0453   $76.05   $76.05   $76.00  
  Purchase #2 $186.85   9.571%   $204.7334   $204.73   $204.75   $204.70  
  Purchase #3 $240.86   11.717%   $269.0816   $269.08   $269.10   $269.10  
  Purchase #4 $177.72   10.562%   $196.4908   $196.49   $196.50   $196.50  
  Purchase #5 $235.56   3.386%   $243.5361   $243.54   $243.55   $243.50  
  Purchase #6 $179.35   3.541%   $185.7008   $185.70   $185.70   $185.70  
  Purchase #7 $119.39   12.232%   $133.9938   $133.99   $134.00   $134.00  
  7 purchase totals = $1,211.12       $1,309.5818   $1,309.58   $1,309.65   $1,309.50