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 $31.38   13.791%   $35.7076   $35.71   $35.70   $35.70  
  Purchase #2 $158.41   13.275%   $179.4389   $179.44   $179.45   $179.40  
  Purchase #3 $113.28   9.159%   $123.6553   $123.66   $123.65   $123.70  
  Purchase #4 $186.72   13.474%   $211.8787   $211.88   $211.90   $211.90  
  Purchase #5 $224.74   10.678%   $248.7377   $248.74   $248.75   $248.70  
  Purchase #6 $186.91   7.848%   $201.5787   $201.58   $201.60   $201.60  
  Purchase #7 $216.93   12.436%   $243.9074   $243.91   $243.90   $243.90  
  7 purchase totals = $1,118.37       $1,244.9043   $1,244.92   $1,244.95   $1,244.90