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 $82.45   13.534%   $93.6088   $93.61   $93.60   $93.60  
  Purchase #2 $21.74   5.638%   $22.9657   $22.97   $22.95   $23.00  
  Purchase #3 $220.28   3.725%   $228.4854   $228.49   $228.50   $228.50  
  Purchase #4 $119.74   13.535%   $135.9468   $135.95   $135.95   $135.90  
  Purchase #5 $162.67   12.846%   $183.5666   $183.57   $183.55   $183.60  
  Purchase #6 $250.27   7.691%   $269.5183   $269.52   $269.50   $269.50  
  Purchase #7 $71.31   4.636%   $74.6159   $74.62   $74.60   $74.60  
  7 purchase totals = $928.46       $1,008.7075   $1,008.73   $1,008.65   $1,008.70