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 $230.76   12.755%   $260.1934   $260.19   $260.20   $260.20  
  Purchase #2 $197.98   6.359%   $210.5695   $210.57   $210.55   $210.60  
  Purchase #3 $123.84   11.650%   $138.2674   $138.27   $138.25   $138.30  
  Purchase #4 $62.94   9.638%   $69.0062   $69.01   $69.00   $69.00  
  Purchase #5 $161.94   10.655%   $179.1947   $179.19   $179.20   $179.20  
  Purchase #6 $226.61   8.680%   $246.2797   $246.28   $246.30   $246.30  
  Purchase #7 $176.67   4.173%   $184.0424   $184.04   $184.05   $184.00  
  7 purchase totals = $1,180.74       $1,287.5533   $1,287.55   $1,287.55   $1,287.60