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 $68.92   6.358%   $73.3019   $73.30   $73.30   $73.30  
  Purchase #2 $97.72   13.312%   $110.7285   $110.73   $110.75   $110.70  
  Purchase #3 $52.42   6.288%   $55.7162   $55.72   $55.70   $55.70  
  Purchase #4 $185.94   9.488%   $203.582   $203.58   $203.60   $203.60  
  Purchase #5 $68.80   7.550%   $73.9944   $73.99   $74.00   $74.00  
  Purchase #6 $56.54   8.803%   $61.5172   $61.52   $61.50   $61.50  
  Purchase #7 $173.34   12.748%   $195.4374   $195.44   $195.45   $195.40  
  7 purchase totals = $703.68       $774.2776   $774.28   $774.30   $774.20