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 $88.58   10.112%   $97.5372   $97.54   $97.55   $97.50  
  Purchase #2 $108.25   3.398%   $111.9283   $111.93   $111.95   $111.90  
  Purchase #3 $171.51   6.305%   $182.3237   $182.32   $182.30   $182.30  
  Purchase #4 $5.46   9.239%   $5.9644   $5.96   $5.95   $6.00  
  Purchase #5 $135.83   12.571%   $152.9052   $152.91   $152.90   $152.90  
  Purchase #6 $246.95   8.444%   $267.8025   $267.80   $267.80   $267.80  
  Purchase #7 $103.55   3.819%   $107.5046   $107.50   $107.50   $107.50  
  7 purchase totals = $860.13       $925.9659   $925.96   $925.95   $925.90