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 $124.73   7.846%   $134.5163   $134.52   $134.50   $134.50  
  Purchase #2 $104.77   13.851%   $119.2817   $119.28   $119.30   $119.30  
  Purchase #3 $197.45   3.869%   $205.0893   $205.09   $205.10   $205.10  
  Purchase #4 $68.45   3.808%   $71.0566   $71.06   $71.05   $71.10  
  Purchase #5 $144.47   4.511%   $150.987   $150.99   $151.00   $151.00  
  Purchase #6 $243.76   10.407%   $269.1281   $269.13   $269.15   $269.10  
  Purchase #7 $93.54   3.871%   $97.1609   $97.16   $97.15   $97.20  
  7 purchase totals = $977.17       $1,047.2199   $1,047.23   $1,047.25   $1,047.30