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 $150.99   12.274%   $169.5225   $169.52   $169.50   $169.50  
  Purchase #2 $201.52   8.542%   $218.7338   $218.73   $218.75   $218.70  
  Purchase #3 $51.53   3.362%   $53.2624   $53.26   $53.25   $53.30  
  Purchase #4 $32.75   7.126%   $35.0838   $35.08   $35.10   $35.10  
  Purchase #5 $183.25   10.583%   $202.6433   $202.64   $202.65   $202.60  
  Purchase #6 $107.51   11.153%   $119.5006   $119.50   $119.50   $119.50  
  Purchase #7 $198.83   3.558%   $205.9044   $205.90   $205.90   $205.90  
  7 purchase totals = $926.38       $1,004.6508   $1,004.63   $1,004.65   $1,004.60