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 $247.64   8.623%   $268.994   $268.99   $269.00   $269.00  
  Purchase #2 $44.67   7.542%   $48.039   $48.04   $48.05   $48.00  
  Purchase #3 $229.25   11.127%   $254.7586   $254.76   $254.75   $254.80  
  Purchase #4 $207.78   7.637%   $223.6482   $223.65   $223.65   $223.60  
  Purchase #5 $169.46   11.844%   $189.5308   $189.53   $189.55   $189.50  
  Purchase #6 $60.53   8.641%   $65.7604   $65.76   $65.75   $65.80  
  Purchase #7 $58.51   4.104%   $60.9113   $60.91   $60.90   $60.90  
  7 purchase totals = $1,017.84       $1,111.6423   $1,111.64   $1,111.65   $1,111.60