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 $53.74   9.149%   $58.6567   $58.66   $58.65   $58.70  
  Purchase #2 $178.38   13.542%   $202.5362   $202.54   $202.55   $202.50  
  Purchase #3 $115.42   9.479%   $126.3607   $126.36   $126.35   $126.40  
  Purchase #4 $247.74   8.158%   $267.9506   $267.95   $267.95   $268.00  
  Purchase #5 $193.84   10.861%   $214.893   $214.89   $214.90   $214.90  
  Purchase #6 $245.95   6.250%   $261.3219   $261.32   $261.30   $261.30  
  Purchase #7 $224.82   8.124%   $243.0844   $243.08   $243.10   $243.10  
  7 purchase totals = $1,259.89       $1,374.8035   $1,374.80   $1,374.80   $1,374.90