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 $57.98   10.402%   $64.0111   $64.01   $64.00   $64.00  
  Purchase #2 $117.90   8.856%   $128.3412   $128.34   $128.35   $128.30  
  Purchase #3 $163.90   5.218%   $172.4523   $172.45   $172.45   $172.50  
  Purchase #4 $221.74   12.253%   $248.9098   $248.91   $248.90   $248.90  
  Purchase #5 $32.38   6.584%   $34.5119   $34.51   $34.50   $34.50  
  Purchase #6 $183.35   6.174%   $194.67   $194.67   $194.65   $194.70  
  Purchase #7 $196.93   7.340%   $211.3847   $211.38   $211.40   $211.40  
  7 purchase totals = $974.18       $1,054.2810   $1,054.27   $1,054.25   $1,054.30