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 $85.91   13.184%   $97.2364   $97.24   $97.25   $97.20  
  Purchase #2 $88.67   8.760%   $96.4375   $96.44   $96.45   $96.40  
  Purchase #3 $163.45   11.253%   $181.843   $181.84   $181.85   $181.80  
  Purchase #4 $115.27   13.138%   $130.4142   $130.41   $130.40   $130.40  
  Purchase #5 $53.37   12.203%   $59.8827   $59.88   $59.90   $59.90  
  Purchase #6 $166.71   9.481%   $182.5158   $182.52   $182.50   $182.50  
  Purchase #7 $218.26   12.699%   $245.9768   $245.98   $246.00   $246.00  
  7 purchase totals = $891.64       $994.3064   $994.31   $994.35   $994.20