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 $210.92   10.751%   $233.596   $233.60   $233.60   $233.60  
  Purchase #2 $231.57   3.462%   $239.587   $239.59   $239.60   $239.60  
  Purchase #3 $81.91   3.397%   $84.6925   $84.69   $84.70   $84.70  
  Purchase #4 $21.70   12.580%   $24.4299   $24.43   $24.45   $24.40  
  Purchase #5 $122.49   5.817%   $129.6152   $129.62   $129.60   $129.60  
  Purchase #6 $56.51   9.764%   $62.0276   $62.03   $62.05   $62.00  
  Purchase #7 $228.76   12.638%   $257.6707   $257.67   $257.65   $257.70  
  7 purchase totals = $953.86       $1,031.6189   $1,031.63   $1,031.65   $1,031.60