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 $58.79   12.769%   $66.2969   $66.30   $66.30   $66.30  
  Purchase #2 $169.37   7.145%   $181.4715   $181.47   $181.45   $181.50  
  Purchase #3 $233.71   10.116%   $257.3521   $257.35   $257.35   $257.40  
  Purchase #4 $225.27   7.102%   $241.2687   $241.27   $241.25   $241.30  
  Purchase #5 $58.49   8.480%   $63.45   $63.45   $63.45   $63.50  
  Purchase #6 $68.47   11.492%   $76.3386   $76.34   $76.35   $76.30  
  Purchase #7 $149.97   13.289%   $169.8995   $169.90   $169.90   $169.90  
  7 purchase totals = $964.07       $1,056.0773   $1,056.08   $1,056.05   $1,056.20