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 $126.95   11.809%   $141.9415   $141.94   $141.95   $141.90  
  Purchase #2 $79.57   5.366%   $83.8397   $83.84   $83.85   $83.80  
  Purchase #3 $136.83   8.678%   $148.7041   $148.70   $148.70   $148.70  
  Purchase #4 $232.49   11.138%   $258.3847   $258.38   $258.40   $258.40  
  Purchase #5 $67.92   4.574%   $71.0267   $71.03   $71.05   $71.00  
  Purchase #6 $220.75   10.432%   $243.7786   $243.78   $243.80   $243.80  
  Purchase #7 $57.93   9.312%   $63.3244   $63.32   $63.30   $63.30  
  7 purchase totals = $922.44       $1,010.9997   $1,010.99   $1,011.05   $1,010.90