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 $65.82   6.724%   $70.2457   $70.25   $70.25   $70.20  
  Purchase #2 $162.66   11.771%   $181.8067   $181.81   $181.80   $181.80  
  Purchase #3 $45.93   8.339%   $49.7601   $49.76   $49.75   $49.80  
  Purchase #4 $89.82   6.341%   $95.5155   $95.52   $95.50   $95.50  
  Purchase #5 $115.87   8.111%   $125.2682   $125.27   $125.25   $125.30  
  Purchase #6 $45.92   5.778%   $48.5733   $48.57   $48.55   $48.60  
  Purchase #7 $206.57   11.422%   $230.1644   $230.16   $230.15   $230.20  
  7 purchase totals = $732.59       $801.3339   $801.34   $801.25   $801.40