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 $164.89   7.462%   $177.1941   $177.19   $177.20   $177.20  
  Purchase #2 $228.98   13.430%   $259.732   $259.73   $259.75   $259.70  
  Purchase #3 $67.52   4.290%   $70.4166   $70.42   $70.40   $70.40  
  Purchase #4 $224.75   4.215%   $234.2232   $234.22   $234.20   $234.20  
  Purchase #5 $104.99   6.112%   $111.407   $111.41   $111.40   $111.40  
  Purchase #6 $93.41   11.822%   $104.4529   $104.45   $104.45   $104.50  
  Purchase #7 $186.29   5.123%   $195.8336   $195.83   $195.85   $195.80  
  7 purchase totals = $1,070.83       $1,153.2594   $1,153.25   $1,153.25   $1,153.20