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 $231.92   13.559%   $263.366   $263.37   $263.35   $263.40  
  Purchase #2 $71.81   11.617%   $80.1522   $80.15   $80.15   $80.20  
  Purchase #3 $43.94   6.493%   $46.793   $46.79   $46.80   $46.80  
  Purchase #4 $126.34   13.340%   $143.1938   $143.19   $143.20   $143.20  
  Purchase #5 $126.43   5.466%   $133.3407   $133.34   $133.35   $133.30  
  Purchase #6 $234.43   10.487%   $259.0147   $259.01   $259.00   $259.00  
  Purchase #7 $173.45   10.226%   $191.187   $191.19   $191.20   $191.20  
  7 purchase totals = $1,008.32       $1,117.0474   $1,117.04   $1,117.05   $1,117.10