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 $246.70   12.151%   $276.6765   $276.68   $276.70   $276.70  
  Purchase #2 $48.65   11.355%   $54.1742   $54.17   $54.15   $54.20  
  Purchase #3 $242.73   12.623%   $273.3698   $273.37   $273.35   $273.40  
  Purchase #4 $247.93   11.310%   $275.9709   $275.97   $275.95   $276.00  
  Purchase #5 $87.77   6.242%   $93.2486   $93.25   $93.25   $93.20  
  Purchase #6 $157.53   9.168%   $171.9724   $171.97   $171.95   $172.00  
  Purchase #7 $194.72   10.396%   $214.9631   $214.96   $214.95   $215.00  
  7 purchase totals = $1,226.03       $1,360.3755   $1,360.37   $1,360.30   $1,360.50