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 $97.54   9.344%   $106.6541   $106.65   $106.65   $106.70  
  Purchase #2 $174.85   4.457%   $182.6431   $182.64   $182.65   $182.60  
  Purchase #3 $114.52   7.658%   $123.2899   $123.29   $123.30   $123.30  
  Purchase #4 $92.99   9.678%   $101.9896   $101.99   $102.00   $102.00  
  Purchase #5 $147.34   8.848%   $160.3766   $160.38   $160.40   $160.40  
  Purchase #6 $169.62   8.298%   $183.6951   $183.70   $183.70   $183.70  
  Purchase #7 $181.81   6.495%   $193.6186   $193.62   $193.60   $193.60  
  7 purchase totals = $978.67       $1,052.2670   $1,052.27   $1,052.30   $1,052.30