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 $244.83   12.432%   $275.2673   $275.27   $275.25   $275.30  
  Purchase #2 $190.31   10.739%   $210.7474   $210.75   $210.75   $210.70  
  Purchase #3 $209.99   9.330%   $229.5821   $229.58   $229.60   $229.60  
  Purchase #4 $25.30   6.737%   $27.0045   $27.00   $27.00   $27.00  
  Purchase #5 $208.88   11.391%   $232.6735   $232.67   $232.65   $232.70  
  Purchase #6 $164.88   8.657%   $179.1537   $179.15   $179.15   $179.20  
  Purchase #7 $124.96   12.134%   $140.1226   $140.12   $140.10   $140.10  
  7 purchase totals = $1,169.15       $1,294.5511   $1,294.54   $1,294.50   $1,294.60