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 $33.81   7.574%   $36.3708   $36.37   $36.35   $36.40  
  Purchase #2 $166.68   9.264%   $182.1212   $182.12   $182.10   $182.10  
  Purchase #3 $237.86   6.485%   $253.2852   $253.29   $253.30   $253.30  
  Purchase #4 $52.97   4.449%   $55.3266   $55.33   $55.35   $55.30  
  Purchase #5 $163.44   7.475%   $175.6571   $175.66   $175.65   $175.70  
  Purchase #6 $161.37   6.291%   $171.5218   $171.52   $171.50   $171.50  
  Purchase #7 $164.35   12.585%   $185.0334   $185.03   $185.05   $185.00  
  7 purchase totals = $980.48       $1,059.3161   $1,059.32   $1,059.30   $1,059.30