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 $119.83   8.718%   $130.2768   $130.28   $130.30   $130.30  
  Purchase #2 $125.44   10.435%   $138.5297   $138.53   $138.55   $138.50  
  Purchase #3 $33.78   11.768%   $37.7552   $37.76   $37.75   $37.80  
  Purchase #4 $16.71   3.131%   $17.2332   $17.23   $17.25   $17.20  
  Purchase #5 $240.26   7.365%   $257.9551   $257.96   $257.95   $258.00  
  Purchase #6 $219.82   10.785%   $243.5276   $243.53   $243.55   $243.50  
  Purchase #7 $237.52   6.117%   $252.0491   $252.05   $252.05   $252.00  
  7 purchase totals = $993.36       $1,077.3267   $1,077.34   $1,077.40   $1,077.30