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 $69.38   8.797%   $75.4834   $75.48   $75.50   $75.50  
  Purchase #2 $37.26   13.235%   $42.1914   $42.19   $42.20   $42.20  
  Purchase #3 $166.83   12.305%   $187.3584   $187.36   $187.35   $187.40  
  Purchase #4 $198.89   4.507%   $207.854   $207.85   $207.85   $207.90  
  Purchase #5 $70.52   7.805%   $76.0241   $76.02   $76.00   $76.00  
  Purchase #6 $29.53   12.866%   $33.3293   $33.33   $33.35   $33.30  
  Purchase #7 $205.67   9.569%   $225.3506   $225.35   $225.35   $225.40  
  7 purchase totals = $778.08       $847.5912   $847.58   $847.60   $847.70