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 $246.78   11.529%   $275.2313   $275.23   $275.25   $275.20  
  Purchase #2 $86.69   6.779%   $92.5667   $92.57   $92.55   $92.60  
  Purchase #3 $66.93   13.828%   $76.1851   $76.19   $76.20   $76.20  
  Purchase #4 $74.73   3.220%   $77.1363   $77.14   $77.15   $77.10  
  Purchase #5 $239.79   7.289%   $257.2683   $257.27   $257.25   $257.30  
  Purchase #6 $179.91   13.851%   $204.8293   $204.83   $204.85   $204.80  
  Purchase #7 $23.56   5.477%   $24.8504   $24.85   $24.85   $24.90  
  7 purchase totals = $918.39       $1,008.0674   $1,008.08   $1,008.10   $1,008.10