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 $56.80   10.790%   $62.9287   $62.93   $62.95   $62.90  
  Purchase #2 $55.74   4.717%   $58.3693   $58.37   $58.35   $58.40  
  Purchase #3 $22.37   7.570%   $24.0634   $24.06   $24.05   $24.10  
  Purchase #4 $248.25   13.427%   $281.5825   $281.58   $281.60   $281.60  
  Purchase #5 $158.95   7.398%   $170.7091   $170.71   $170.70   $170.70  
  Purchase #6 $179.74   10.555%   $198.7116   $198.71   $198.70   $198.70  
  Purchase #7 $85.52   5.757%   $90.4434   $90.44   $90.45   $90.40  
  7 purchase totals = $807.37       $886.8080   $886.80   $886.80   $886.80