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 $24.68   8.444%   $26.764   $26.76   $26.75   $26.80  
  Purchase #2 $212.83   5.647%   $224.8485   $224.85   $224.85   $224.80  
  Purchase #3 $32.33   3.184%   $33.3594   $33.36   $33.35   $33.40  
  Purchase #4 $198.64   13.689%   $225.8318   $225.83   $225.85   $225.80  
  Purchase #5 $161.49   6.396%   $171.8189   $171.82   $171.80   $171.80  
  Purchase #6 $58.26   3.865%   $60.5117   $60.51   $60.50   $60.50  
  Purchase #7 $154.95   13.140%   $175.3104   $175.31   $175.30   $175.30  
  7 purchase totals = $843.18       $918.4447   $918.44   $918.40   $918.40