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 $59.47   3.745%   $61.6972   $61.70   $61.70   $61.70  
  Purchase #2 $109.87   3.188%   $113.3727   $113.37   $113.35   $113.40  
  Purchase #3 $100.30   6.805%   $107.1254   $107.13   $107.15   $107.10  
  Purchase #4 $153.80   7.230%   $164.9197   $164.92   $164.90   $164.90  
  Purchase #5 $58.26   4.126%   $60.6638   $60.66   $60.65   $60.70  
  Purchase #6 $170.49   7.598%   $183.4438   $183.44   $183.45   $183.40  
  Purchase #7 $246.36   9.718%   $270.3013   $270.30   $270.30   $270.30  
  7 purchase totals = $898.55       $961.5239   $961.52   $961.50   $961.50