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 $119.89   11.798%   $134.0346   $134.03   $134.05   $134.00  
  Purchase #2 $180.32   11.629%   $201.2894   $201.29   $201.30   $201.30  
  Purchase #3 $132.63   7.762%   $142.9247   $142.92   $142.90   $142.90  
  Purchase #4 $169.74   4.692%   $177.7042   $177.70   $177.70   $177.70  
  Purchase #5 $237.54   10.678%   $262.9045   $262.90   $262.90   $262.90  
  Purchase #6 $192.86   10.196%   $212.524   $212.52   $212.50   $212.50  
  Purchase #7 $25.43   12.541%   $28.6192   $28.62   $28.60   $28.60  
  7 purchase totals = $1,058.41       $1,160.0006   $1,159.98   $1,159.95   $1,159.90