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 $58.51   6.633%   $62.391   $62.39   $62.40   $62.40  
  Purchase #2 $169.35   6.713%   $180.7185   $180.72   $180.70   $180.70  
  Purchase #3 $16.36   11.814%   $18.2928   $18.29   $18.30   $18.30  
  Purchase #4 $90.86   11.231%   $101.0645   $101.06   $101.05   $101.10  
  Purchase #5 $237.49   11.113%   $263.8823   $263.88   $263.90   $263.90  
  Purchase #6 $160.55   11.309%   $178.7066   $178.71   $178.70   $178.70  
  Purchase #7 $161.94   8.389%   $175.5251   $175.53   $175.55   $175.50  
  7 purchase totals = $895.06       $980.5808   $980.58   $980.60   $980.60