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 $61.48   9.537%   $67.3433   $67.34   $67.35   $67.30  
  Purchase #2 $244.61   11.119%   $271.8082   $271.81   $271.80   $271.80  
  Purchase #3 $235.31   9.712%   $258.1633   $258.16   $258.15   $258.20  
  Purchase #4 $97.41   4.770%   $102.0565   $102.06   $102.05   $102.10  
  Purchase #5 $215.99   12.678%   $243.3732   $243.37   $243.35   $243.40  
  Purchase #6 $246.94   6.809%   $263.7541   $263.75   $263.75   $263.80  
  Purchase #7 $246.65   12.500%   $277.4813   $277.48   $277.50   $277.50  
  7 purchase totals = $1,348.39       $1,483.9799   $1,483.97   $1,483.95   $1,484.10