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 $142.92   8.383%   $154.901   $154.90   $154.90   $154.90  
  Purchase #2 $97.79   4.236%   $101.9324   $101.93   $101.95   $101.90  
  Purchase #3 $182.87   4.445%   $190.9986   $191.00   $191.00   $191.00  
  Purchase #4 $50.77   9.871%   $55.7815   $55.78   $55.80   $55.80  
  Purchase #5 $205.98   13.626%   $234.0468   $234.05   $234.05   $234.00  
  Purchase #6 $49.65   12.576%   $55.894   $55.89   $55.90   $55.90  
  Purchase #7 $222.44   11.279%   $247.529   $247.53   $247.55   $247.50  
  7 purchase totals = $952.42       $1,041.0833   $1,041.08   $1,041.15   $1,041.00