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 $77.27   13.727%   $87.8769   $87.88   $87.90   $87.90  
  Purchase #2 $67.64   4.196%   $70.4782   $70.48   $70.50   $70.50  
  Purchase #3 $107.52   7.692%   $115.7904   $115.79   $115.80   $115.80  
  Purchase #4 $129.58   7.136%   $138.8268   $138.83   $138.85   $138.80  
  Purchase #5 $132.78   5.142%   $139.6075   $139.61   $139.60   $139.60  
  Purchase #6 $125.25   7.468%   $134.6037   $134.60   $134.60   $134.60  
  Purchase #7 $45.90   11.450%   $51.1556   $51.16   $51.15   $51.20  
  7 purchase totals = $685.94       $738.3391   $738.35   $738.40   $738.40