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 $239.77   3.126%   $247.2652   $247.27   $247.25   $247.30  
  Purchase #2 $175.77   6.655%   $187.4675   $187.47   $187.45   $187.50  
  Purchase #3 $159.58   9.473%   $174.697   $174.70   $174.70   $174.70  
  Purchase #4 $238.82   7.728%   $257.276   $257.28   $257.30   $257.30  
  Purchase #5 $223.52   5.817%   $236.5222   $236.52   $236.50   $236.50  
  Purchase #6 $134.94   6.108%   $143.1821   $143.18   $143.20   $143.20  
  Purchase #7 $130.92   11.822%   $146.3974   $146.40   $146.40   $146.40  
  7 purchase totals = $1,303.32       $1,392.8074   $1,392.82   $1,392.80   $1,392.90