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 $146.25   10.642%   $161.8139   $161.81   $161.80   $161.80  
  Purchase #2 $181.65   8.639%   $197.3427   $197.34   $197.35   $197.30  
  Purchase #3 $207.96   12.293%   $233.5245   $233.52   $233.50   $233.50  
  Purchase #4 $140.42   7.651%   $151.1635   $151.16   $151.15   $151.20  
  Purchase #5 $89.49   13.116%   $101.2275   $101.23   $101.25   $101.20  
  Purchase #6 $79.72   6.572%   $84.9592   $84.96   $84.95   $85.00  
  Purchase #7 $94.51   10.548%   $104.4789   $104.48   $104.50   $104.50  
  7 purchase totals = $940.00       $1,034.5102   $1,034.50   $1,034.50   $1,034.50