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 $48.66   5.874%   $51.5183   $51.52   $51.50   $51.50  
  Purchase #2 $15.53   7.446%   $16.6864   $16.69   $16.70   $16.70  
  Purchase #3 $231.66   8.762%   $251.958   $251.96   $251.95   $252.00  
  Purchase #4 $206.32   13.184%   $233.5212   $233.52   $233.50   $233.50  
  Purchase #5 $219.37   12.595%   $246.9997   $247.00   $247.00   $247.00  
  Purchase #6 $215.94   5.584%   $227.9981   $228.00   $228.00   $228.00  
  Purchase #7 $185.88   7.726%   $200.2411   $200.24   $200.25   $200.20  
  7 purchase totals = $1,123.36       $1,228.9228   $1,228.93   $1,228.90   $1,228.90