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 $63.78   12.293%   $71.6205   $71.62   $71.60   $71.60  
  Purchase #2 $144.96   6.413%   $154.2563   $154.26   $154.25   $154.30  
  Purchase #3 $122.37   12.568%   $137.7495   $137.75   $137.75   $137.70  
  Purchase #4 $103.71   12.627%   $116.8055   $116.81   $116.80   $116.80  
  Purchase #5 $235.26   13.711%   $267.5165   $267.52   $267.50   $267.50  
  Purchase #6 $111.51   6.202%   $118.4259   $118.43   $118.45   $118.40  
  Purchase #7 $122.58   9.426%   $134.1344   $134.13   $134.15   $134.10  
  7 purchase totals = $904.17       $1,000.5086   $1,000.52   $1,000.50   $1,000.40