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 $24.79   7.667%   $26.6906   $26.69   $26.70   $26.70  
  Purchase #2 $177.48   9.197%   $193.8028   $193.80   $193.80   $193.80  
  Purchase #3 $239.65   13.617%   $272.2831   $272.28   $272.30   $272.30  
  Purchase #4 $196.57   5.681%   $207.7371   $207.74   $207.75   $207.70  
  Purchase #5 $133.31   9.808%   $146.385   $146.39   $146.40   $146.40  
  Purchase #6 $84.60   11.352%   $94.2038   $94.20   $94.20   $94.20  
  Purchase #7 $103.52   3.373%   $107.0117   $107.01   $107.00   $107.00  
  7 purchase totals = $959.92       $1,048.1141   $1,048.11   $1,048.15   $1,048.10