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 $189.94   8.421%   $205.9348   $205.93   $205.95   $205.90  
  Purchase #2 $167.37   11.662%   $186.8887   $186.89   $186.90   $186.90  
  Purchase #3 $39.72   12.767%   $44.7911   $44.79   $44.80   $44.80  
  Purchase #4 $234.87   11.131%   $261.0134   $261.01   $261.00   $261.00  
  Purchase #5 $34.98   9.597%   $38.337   $38.34   $38.35   $38.30  
  Purchase #6 $190.41   11.631%   $212.5566   $212.56   $212.55   $212.60  
  Purchase #7 $10.46   3.699%   $10.8469   $10.85   $10.85   $10.80  
  7 purchase totals = $867.75       $960.3685   $960.37   $960.40   $960.30