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 $119.93   6.191%   $127.3549   $127.35   $127.35   $127.40  
  Purchase #2 $16.26   7.273%   $17.4426   $17.44   $17.45   $17.40  
  Purchase #3 $229.95   7.265%   $246.6559   $246.66   $246.65   $246.70  
  Purchase #4 $101.41   13.473%   $115.073   $115.07   $115.05   $115.10  
  Purchase #5 $239.25   3.622%   $247.9156   $247.92   $247.90   $247.90  
  Purchase #6 $141.57   5.267%   $149.0265   $149.03   $149.05   $149.00  
  Purchase #7 $116.52   5.335%   $122.7363   $122.74   $122.75   $122.70  
  7 purchase totals = $964.89       $1,026.2048   $1,026.21   $1,026.20   $1,026.20