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 $118.89   7.446%   $127.7425   $127.74   $127.75   $127.70  
  Purchase #2 $222.91   3.812%   $231.4073   $231.41   $231.40   $231.40  
  Purchase #3 $44.52   12.385%   $50.0338   $50.03   $50.05   $50.00  
  Purchase #4 $101.44   11.347%   $112.9504   $112.95   $112.95   $113.00  
  Purchase #5 $39.95   11.417%   $44.5111   $44.51   $44.50   $44.50  
  Purchase #6 $227.62   13.554%   $258.4716   $258.47   $258.45   $258.50  
  Purchase #7 $209.30   7.166%   $224.2984   $224.30   $224.30   $224.30  
  7 purchase totals = $964.63       $1,049.4151   $1,049.41   $1,049.40   $1,049.40