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 $94.96   10.157%   $104.6051   $104.61   $104.60   $104.60  
  Purchase #2 $202.38   5.477%   $213.4644   $213.46   $213.45   $213.50  
  Purchase #3 $151.84   5.528%   $160.2337   $160.23   $160.25   $160.20  
  Purchase #4 $157.91   5.766%   $167.0151   $167.02   $167.00   $167.00  
  Purchase #5 $127.65   8.537%   $138.5475   $138.55   $138.55   $138.50  
  Purchase #6 $84.52   8.738%   $91.9054   $91.91   $91.90   $91.90  
  Purchase #7 $44.71   8.658%   $48.581   $48.58   $48.60   $48.60  
  7 purchase totals = $863.97       $924.3522   $924.36   $924.35   $924.30