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 $23.36   13.706%   $26.5617   $26.56   $26.55   $26.60  
  Purchase #2 $89.84   7.184%   $96.2941   $96.29   $96.30   $96.30  
  Purchase #3 $6.76   8.729%   $7.3501   $7.35   $7.35   $7.40  
  Purchase #4 $130.95   5.822%   $138.5739   $138.57   $138.55   $138.60  
  Purchase #5 $236.29   6.554%   $251.7764   $251.78   $251.80   $251.80  
  Purchase #6 $92.58   9.473%   $101.3501   $101.35   $101.35   $101.40  
  Purchase #7 $143.78   11.737%   $160.6555   $160.66   $160.65   $160.70  
  7 purchase totals = $723.56       $782.5618   $782.56   $782.55   $782.80