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 $144.29   12.660%   $162.5571   $162.56   $162.55   $162.60  
  Purchase #2 $207.92   11.241%   $231.2923   $231.29   $231.30   $231.30  
  Purchase #3 $124.27   9.206%   $135.7103   $135.71   $135.70   $135.70  
  Purchase #4 $242.93   9.171%   $265.2091   $265.21   $265.20   $265.20  
  Purchase #5 $59.66   4.268%   $62.2063   $62.21   $62.20   $62.20  
  Purchase #6 $165.78   6.237%   $176.1197   $176.12   $176.10   $176.10  
  Purchase #7 $219.28   5.368%   $231.051   $231.05   $231.05   $231.10  
  7 purchase totals = $1,164.13       $1,264.1458   $1,264.15   $1,264.10   $1,264.20