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 $184.48   12.833%   $208.1543   $208.15   $208.15   $208.20  
  Purchase #2 $146.30   5.708%   $154.6508   $154.65   $154.65   $154.70  
  Purchase #3 $76.52   10.773%   $84.7635   $84.76   $84.75   $84.80  
  Purchase #4 $216.95   5.330%   $228.5134   $228.51   $228.50   $228.50  
  Purchase #5 $145.62   9.806%   $159.8995   $159.90   $159.90   $159.90  
  Purchase #6 $136.67   4.314%   $142.5659   $142.57   $142.55   $142.60  
  Purchase #7 $141.31   13.174%   $159.9262   $159.93   $159.95   $159.90  
  7 purchase totals = $1,047.85       $1,138.4736   $1,138.47   $1,138.45   $1,138.60