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 $228.45   13.816%   $260.0127   $260.01   $260.00   $260.00  
  Purchase #2 $63.29   13.600%   $71.8974   $71.90   $71.90   $71.90  
  Purchase #3 $22.74   6.590%   $24.2386   $24.24   $24.25   $24.20  
  Purchase #4 $235.39   10.267%   $259.5575   $259.56   $259.55   $259.60  
  Purchase #5 $150.76   5.591%   $159.189   $159.19   $159.20   $159.20  
  Purchase #6 $232.59   3.364%   $240.4143   $240.41   $240.40   $240.40  
  Purchase #7 $7.71   10.837%   $8.5455   $8.55   $8.55   $8.50  
  7 purchase totals = $940.93       $1,023.8550   $1,023.86   $1,023.85   $1,023.80