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 $61.61   6.552%   $65.6467   $65.65   $65.65   $65.60  
  Purchase #2 $221.50   5.310%   $233.2617   $233.26   $233.25   $233.30  
  Purchase #3 $68.55   6.645%   $73.1051   $73.11   $73.10   $73.10  
  Purchase #4 $235.95   8.545%   $256.1119   $256.11   $256.10   $256.10  
  Purchase #5 $109.46   8.564%   $118.8342   $118.83   $118.85   $118.80  
  Purchase #6 $169.88   11.482%   $189.3856   $189.39   $189.40   $189.40  
  Purchase #7 $212.74   5.668%   $224.7981   $224.80   $224.80   $224.80  
  7 purchase totals = $1,079.69       $1,161.1433   $1,161.15   $1,161.15   $1,161.10