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 $245.79   9.481%   $269.0933   $269.09   $269.10   $269.10  
  Purchase #2 $82.60   3.338%   $85.3572   $85.36   $85.35   $85.40  
  Purchase #3 $196.35   6.414%   $208.9439   $208.94   $208.95   $208.90  
  Purchase #4 $203.49   4.646%   $212.9441   $212.94   $212.95   $212.90  
  Purchase #5 $94.40   10.180%   $104.0099   $104.01   $104.00   $104.00  
  Purchase #6 $195.90   3.258%   $202.2824   $202.28   $202.30   $202.30  
  Purchase #7 $156.28   9.363%   $170.9125   $170.91   $170.90   $170.90  
  7 purchase totals = $1,174.81       $1,253.5433   $1,253.53   $1,253.55   $1,253.50