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 $236.93   12.828%   $267.3234   $267.32   $267.30   $267.30  
  Purchase #2 $5.29   12.378%   $5.9448   $5.94   $5.95   $5.90  
  Purchase #3 $34.99   11.605%   $39.0506   $39.05   $39.05   $39.10  
  Purchase #4 $106.56   3.795%   $110.604   $110.60   $110.60   $110.60  
  Purchase #5 $147.74   6.271%   $157.0048   $157.00   $157.00   $157.00  
  Purchase #6 $238.80   12.695%   $269.1157   $269.12   $269.10   $269.10  
  Purchase #7 $183.83   10.552%   $203.2277   $203.23   $203.25   $203.20  
  7 purchase totals = $954.14       $1,052.2710   $1,052.26   $1,052.25   $1,052.20