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 $140.69   9.516%   $154.0781   $154.08   $154.10   $154.10  
  Purchase #2 $214.48   4.136%   $223.3509   $223.35   $223.35   $223.40  
  Purchase #3 $72.66   13.588%   $82.533   $82.53   $82.55   $82.50  
  Purchase #4 $132.88   8.190%   $143.7629   $143.76   $143.75   $143.80  
  Purchase #5 $193.45   6.586%   $206.1906   $206.19   $206.20   $206.20  
  Purchase #6 $127.52   8.702%   $138.6168   $138.62   $138.60   $138.60  
  Purchase #7 $45.74   13.528%   $51.9277   $51.93   $51.95   $51.90  
  7 purchase totals = $927.42       $1,000.4600   $1,000.46   $1,000.50   $1,000.50