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 $53.66   5.578%   $56.6532   $56.65   $56.65   $56.70  
  Purchase #2 $156.49   11.485%   $174.4629   $174.46   $174.45   $174.50  
  Purchase #3 $181.31   3.382%   $187.4419   $187.44   $187.45   $187.40  
  Purchase #4 $105.45   11.699%   $117.7866   $117.79   $117.80   $117.80  
  Purchase #5 $136.46   5.838%   $144.4265   $144.43   $144.45   $144.40  
  Purchase #6 $247.72   7.467%   $266.2173   $266.22   $266.20   $266.20  
  Purchase #7 $220.95   11.140%   $245.5638   $245.56   $245.55   $245.60  
  7 purchase totals = $1,102.04       $1,192.5522   $1,192.55   $1,192.55   $1,192.60