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 $206.26   12.757%   $232.5726   $232.57   $232.55   $232.60  
  Purchase #2 $241.59   13.403%   $273.9703   $273.97   $273.95   $274.00  
  Purchase #3 $25.36   5.690%   $26.803   $26.80   $26.80   $26.80  
  Purchase #4 $49.79   11.711%   $55.6209   $55.62   $55.60   $55.60  
  Purchase #5 $54.40   4.155%   $56.6603   $56.66   $56.65   $56.70  
  Purchase #6 $221.35   10.339%   $244.2354   $244.24   $244.25   $244.20  
  Purchase #7 $246.85   3.540%   $255.5885   $255.59   $255.60   $255.60  
  7 purchase totals = $1,045.60       $1,145.4510   $1,145.45   $1,145.40   $1,145.50