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 $114.76   7.482%   $123.3463   $123.35   $123.35   $123.30  
  Purchase #2 $246.96   4.341%   $257.6805   $257.68   $257.70   $257.70  
  Purchase #3 $190.44   6.546%   $202.9062   $202.91   $202.90   $202.90  
  Purchase #4 $67.84   4.330%   $70.7775   $70.78   $70.80   $70.80  
  Purchase #5 $161.39   4.720%   $169.0076   $169.01   $169.00   $169.00  
  Purchase #6 $48.49   12.628%   $54.6133   $54.61   $54.60   $54.60  
  Purchase #7 $66.59   4.133%   $69.3422   $69.34   $69.35   $69.30  
  7 purchase totals = $896.47       $947.6736   $947.68   $947.70   $947.60