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 $22.84   7.597%   $24.5752   $24.58   $24.60   $24.60  
  Purchase #2 $36.76   13.248%   $41.63   $41.63   $41.65   $41.60  
  Purchase #3 $61.47   13.673%   $69.8748   $69.87   $69.85   $69.90  
  Purchase #4 $82.34   5.319%   $86.7197   $86.72   $86.70   $86.70  
  Purchase #5 $140.91   3.575%   $145.9475   $145.95   $145.95   $145.90  
  Purchase #6 $247.79   5.199%   $260.6726   $260.67   $260.65   $260.70  
  Purchase #7 $243.69   9.425%   $266.6578   $266.66   $266.65   $266.70  
  7 purchase totals = $835.80       $896.0776   $896.08   $896.05   $896.10