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 $61.36   4.867%   $64.3464   $64.35   $64.35   $64.30  
  Purchase #2 $245.39   3.103%   $253.0045   $253.00   $253.00   $253.00  
  Purchase #3 $75.90   6.245%   $80.64   $80.64   $80.65   $80.60  
  Purchase #4 $96.77   9.650%   $106.1083   $106.11   $106.10   $106.10  
  Purchase #5 $50.78   5.291%   $53.4668   $53.47   $53.45   $53.50  
  Purchase #6 $113.58   5.118%   $119.393   $119.39   $119.40   $119.40  
  Purchase #7 $132.83   13.610%   $150.9082   $150.91   $150.90   $150.90  
  7 purchase totals = $776.61       $827.8672   $827.87   $827.85   $827.80