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 $108.52   10.202%   $119.5912   $119.59   $119.60   $119.60  
  Purchase #2 $80.89   7.146%   $86.6704   $86.67   $86.65   $86.70  
  Purchase #3 $70.68   9.363%   $77.2978   $77.30   $77.30   $77.30  
  Purchase #4 $106.40   13.771%   $121.0523   $121.05   $121.05   $121.10  
  Purchase #5 $124.47   5.452%   $131.2561   $131.26   $131.25   $131.30  
  Purchase #6 $46.67   9.459%   $51.0845   $51.08   $51.10   $51.10  
  Purchase #7 $229.26   13.644%   $260.5402   $260.54   $260.55   $260.50  
  7 purchase totals = $766.89       $847.4925   $847.49   $847.50   $847.60