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 $203.94   11.229%   $226.8404   $226.84   $226.85   $226.80  
  Purchase #2 $37.64   9.380%   $41.1706   $41.17   $41.15   $41.20  
  Purchase #3 $174.69   10.619%   $193.2403   $193.24   $193.25   $193.20  
  Purchase #4 $113.69   11.288%   $126.5233   $126.52   $126.50   $126.50  
  Purchase #5 $148.45   7.137%   $159.0449   $159.04   $159.05   $159.00  
  Purchase #6 $237.72   9.186%   $259.557   $259.56   $259.55   $259.60  
  Purchase #7 $72.80   3.377%   $75.2585   $75.26   $75.25   $75.30  
  7 purchase totals = $988.93       $1,081.6350   $1,081.63   $1,081.60   $1,081.60