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 $61.96   11.700%   $69.2093   $69.21   $69.20   $69.20  
  Purchase #2 $182.59   12.353%   $205.1453   $205.15   $205.15   $205.10  
  Purchase #3 $51.64   3.147%   $53.2651   $53.27   $53.25   $53.30  
  Purchase #4 $243.60   10.551%   $269.3022   $269.30   $269.30   $269.30  
  Purchase #5 $39.59   7.349%   $42.4995   $42.50   $42.50   $42.50  
  Purchase #6 $135.39   6.466%   $144.1443   $144.14   $144.15   $144.10  
  Purchase #7 $197.79   7.541%   $212.7053   $212.71   $212.70   $212.70  
  7 purchase totals = $912.56       $996.2710   $996.28   $996.25   $996.20