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 $239.66   8.773%   $260.6854   $260.69   $260.70   $260.70  
  Purchase #2 $56.41   7.708%   $60.7581   $60.76   $60.75   $60.80  
  Purchase #3 $107.87   4.870%   $113.1233   $113.12   $113.10   $113.10  
  Purchase #4 $161.52   10.169%   $177.945   $177.95   $177.95   $177.90  
  Purchase #5 $85.95   4.196%   $89.5565   $89.56   $89.55   $89.60  
  Purchase #6 $43.93   4.175%   $45.7641   $45.76   $45.75   $45.80  
  Purchase #7 $102.31   6.474%   $108.9335   $108.93   $108.95   $108.90  
  7 purchase totals = $797.65       $856.7659   $856.77   $856.75   $856.80